Abstract In response to the 2013 Update of the European Strategy for Particle Physics, the Future Circular Collider (FCC) study was launched, as an international collaboration hosted by CERN. This study covers a highest-luminosity high-energy lepton collider (FCC-ee) and an energy-frontier hadron collider (FCC-hh), which could, successively, be installed in the same 100 km tunnel. The scientific capabilities of the integrated FCC programme would serve the worldwide community throughout the 21st century. The FCC study also investigates an LHC energy upgrade, using FCC-hh technology. This document constitutes the second volume of the FCC Conceptual Design Report, devoted to the electron-positron collider FCC-ee. After summarizing the physics discovery opportunities, it presents the accelerator design, performance reach, a staged operation scenario, the underlying technologies, civil engineering, technical infrastructure, and an implementation plan. FCC-ee can be built with today's technology. Most of the FCC-ee infrastructure could be reused for FCC-hh. Combining concepts from past and present lepton colliders and adding a few novel elements, the FCC-ee design promises outstandingly high luminosity. This will make the FCC-ee a unique precision instrument to study the heaviest known particles (Z, W and H bosons and the top quark), offering great direct and indirect sensitivity to new physics. © 2019, The Author(s). ; Istanbul Üniversitesi: 3 Istituto Nazionale di Fisica Nucleare Joint Institute for Nuclear Research Istituto Nazionale di Fisica Nucleare CNRS/IN2P3/UPSUD/ LAL University of Oxford INFN CT Kyoto University Kennesaw State University Kangnung National University Joint Institute for Nuclear Research Korea Institute of Toxicology King's College London Islamic Azad University Fondation Louvain CA Chinese Academy of Agricultural Sciences 2 Instituto Nazionale di Fisica Nucleare Kyungpook National University Universidad de Guanajuato High Magnetic Field Laboratory, Chinese Academy of Sciences Nuclear Physics Shenyang Normal University Princeton University, Princeton Stony Brook University: TU Darmstadt University of Tokyo Monash University National and Kapodistrian University of Athens Peking University Trinity College Dublin University of Pittsburgh, Pitt Tsinghua University Universidade do Estado do Rio de Janeiro ES National Research Nuclear University MEPhI Institute for Research in Fundamental Sciences Tel Aviv University Princeton University, Princeton United States Pharmacopeia Tokyo Institute of Technology University of Delhi Tokyo Institute of Technology Technische Universität Dresden: TU Dresden Dalian Institute of Chemical Physics National Rehabilitation Center National Research Center "Kurchatov Institute" Loughborough University Eidgenössische Technische Hochschule Zürich: RWTH Royal Holloway, University of London Trinity College Dublin Scuola Internazionale Superiore di Studi Avanzati Technische Universitat Wien, TU Wien Universidade do Estado do Rio de Janeiro Massachusetts Institute of Technology: MIT Mount Allison University Novosibirsk State Technical University Technische Universität Berlin Pusan National University University of Glasgow National Intelligence University Northwestern University Shahid Beheshti University of Medical Sciences Rutgers, The State University of New Jersey: UNIROMA1 Kingston Technology Nankai University Pennsylvania State University: PSU Royal Holloway, University of London Stanford University Bauman Moscow State Technical University: MSU Florida State University Institute for Research in Fundamental Sciences Lawrence Berkeley National Laboratory, Berkeley Lab Shanghai Jiao Tong University PSI SLAC Natural History Museum University of Chicago University of Cincinnati University of Illinois University of Birmingham University of Cambridge University of California, San Diego University of California, Santa Barbara University of California, Santa Cruz University of Florida City, University of London, City University of California: UCI UCB University College Dublin University of Bristol Health Effects Institute University of California, Santa Barbara University of California, Santa Cruz Sapienza Università di Roma: UNIROMA1, UNIROMA2, UNIROMA3 University of Illinois at Urbana-Champaign Universidade Federal do Rio de Janeiro Departament d'Innovació, Universitats i Empresa, Generalitat de Catalunya: UCL, UC, TW, TU, UA University of California, Irvine: UCSD Università degli Studi di Firenze University of California Berkeley, UC Berkeley University of Arizona Secrétariat Général pour les Affaires Régionales, Etat en Région Aquitaine Secrétariat Général pour les Affaires Régionales, Etat en Région Aquitaine École Polytechnique Fédérale de Lausanne Bundesamt für Energie Seventh Framework Programme: 312453, EuCARD-2 777563, 730871, 654305 European Synchrotron Radiation Facility European Synchrotron Radiation Facility ; 111 Istanbul Aydin University (IAU), Istanbul, Turkey 112 Istanbul University (IÜ), Istanbul, Turkey 113 Istituto Nazionale di Fisica Nucleare, Gruppo Collegato di Salerno – Sezione di Napoli (INFN SA), Salerno, Italy 114Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali del Gran Sasso (INFN LNGS), Assergi (L'Aquila), Italy 115Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Frascati (INFN LNF), Frascati, Italy 116Istituto Nazionale di Fisica Nucleare, Laboratori Nazionali di Legnaro (INFN LNLN), Legnaro, Italy 117 Istituto Nazionale di Fisica Nucleare Sezione di Bari (INFN BA), Bari, Italy 118 Istituto Nazionale di Fisica Nucleare, Sezione di Bologna (INFN BO), Bologna, Italy 119 Istituto Nazionale di Fisica Nucleare, Sezione di Cagliari (INFN CA), Cagliari, Italy 120 Istituto Nazionale di Fisica Nucleare, Sezione di Catania (INFN CT), Catania, Italy 121 Istituto Nazionale di Fisica Nucleare, Sezione di Cosenza (INFN CS), Cosenza, Italy 122 Istituto Nazionale di Fisica Nucleare, Sezione di Ferrara (INFN FE), Ferrara, Italy 123 Istituto Nazionale di Fisica Nucleare, Sezione di Firenze (INFN FI), Florence, Italy 124 Istituto Nazionale di Fisica Nucleare, Sezione di Genova (INFN GE), Genoa, Italy 125 Istituto Nazionale di Fisica Nucleare, Sezione di Lecce (INFN LE), Lecce, Italy 126Istituto Nazionale di Fisica Nucleare, Sezione di Milano Bicocca (INFN MIB), Milan, Italy 127 Istituto Nazionale di Fisica Nucleare, Sezione di Milano (INFN MI), Milan, Italy 128 Istituto Nazionale di Fisica Nucleare, Sezione di Napoli (INFN NA), Naples, Italy 129 Istituto Nazionale di Fisica Nucleare, Sezione di Padova (INFN PD), Padua, Italy 130 Istituto Nazionale di Fisica Nucleare, Sezione di Pavia (INFN PV), Pavia, Italy 131 Istituto Nazionale di Fisica Nucleare, Sezione di Perugia (INFN PG), Perugia, Italy 132Istituto Nazionale di Fisica Nucleare, Sezione di Pisa, Università di Pisa (INFN PI), Pisa, Italy 133 Istituto Nazionale di Fisica Nucleare, Sezione di Roma 1 (INFN Roma 1), Rome, Italy 134Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tor Vergata (INFN Roma 2), Rome, Italy 135 Istituto Nazionale di Fisica Nucleare, Sezione di Roma Tre (INFN Roma 3), Rome, Italy 136 Istituto Nazionale di Fisica Nucleare, Sezione di Torino (INFN TO), Turin, Italy 137 Istituto Nazionale di Fisica Nucleare, Sezione di Trieste (INFN TS), Trieste, Italy 138 ITER (ITER), Cadarache, France 139 Ivane Javakhishvili T'bilisi State University (TSU), T'bilisi, Georgia 140 Izmir University of Economics (IUE), Izmir, Turkey 141 Johannes-Gutenberg-Universität (JGU), Mainz, Germany 142 John Adams Institute for Accelerator Science, The Chancellor, Masters and Scholars of the University of Oxford (JAI), Oxford, UK 143 Joint Institute for Nuclear Research (JINR), Dubna, Russia 144 Julius-Maximilians-Universität Würzburg (UWUERZBURG), Würzburg, Germany 145 Kahramanmaras Sutcu Imam University (KSU), Kahramanmaras, Turkey 146 Karlsruher Institut für Technologie (KIT), Karlsruhe, Germany 147 Katholieke Universiteit Leuven Research & Development (LRD), Louvain, Belgium 148 Key Laboratory of Theoretical Physics, Chinese Academy of Science (SKLTP ITP CAS), Beijing, P.R. China 149 King's College London (KCL), London, UK 150 Kyoto University (Kyodai), Kyoto, Japan 151 Kyungpook National University (KNU), Sankyuk-dong, Republic of Korea 152Laboratoire d'Annecy-Le-Vieux de Physique des Particules (CNRS/IN2P3/LAPP), Annecy, France 153 Laboratoire de l'Accélérateur Linéaire, Universitéde Paris Sud (CNRS/IN2P3/UPSUD/ LAL), Orsay, France 154 Laboratoire de Physique Nucléaire et de Hautes Energies (LPNHE), Paris, France -- 155Laboratoire de Physique Subatomique et de Cosmologie Grenoble (LPSC), Grenoble, France 156Laboratoire de Physique Théorique et Hautes Energies (CNRS/Sorbonne/LPTHE), Paris, France 157 Laboratoire Leprince-Ringuet, Ecole Polytechnique (LLR), Palaiseau, France 158 Laboratório de Instrumentac¸ão e Física Experimental de Partículas (LIP), Lisbon, Portugal 159 Latitude Durable (LD), Geneva, Switzerland 160 Lawrence Berkeley National Laboratory (LBNL), Berkeley, CA, USA 161 Linde Kryotechnik AG (Linde), Pfungen, Switzerland 162 Loughborough University (LBoro), Loughborough, UK 163 Ludwig Maximilians University of Munich (LMU), Munich, Germany 164 Luvata Pori Oy (Luvata), Pori, Finland 165 MAN Energy Solutions Schweiz AG (MAN ES), Zürich, Switzerland 166 Marian Smoluchowski Institute of Physics, Jagiellonian University (UJ), Kraków, Poland 167 Massachusetts Institute of Technology (MIT), Cambridge, MA, USA 168 Max-Planck-Institut für Kernphysik (MPIK), Heidelberg, Germany 169 Max-Planck-Institut für Physik (MPP), Munich, Germany 170 Ministère de l'Europe et des Affaires étrangères (MEAE), Paris, France 171 Monash University (Monash), Melbourne, Australia 172 MTA Wigner Research Centre for Physics (Wigner), Budapest, Hungary 173 Mustafa Kemal Üniversitesi (MKU), Hatay, Turkey 174 Nankai University (NKU), Tianjin, P.R. China 175 Nationaal instituut voor subatomaire fysica (NIKHEF), Amsterdam, The Netherlands 176 National Centre for Scientific Research Demokritos (NCSRD), Athens, Greece 177National High Magnetic Field Laboratory, Florida State University (MagLab), Tallahassee, FL, USA 178 National Institute of Chemical Physics and Biophysics (NICPB), Tallin, Estonia 179 National Research Center Kurchatov Institute (NRCKI), Moscow, Russia 180 National Research Nuclear University MEPhI (MEPhI), Moscow, Russia 181 National Science Centre Kharkov Institute of Physics and Technology (KIPT), Kharkov, Ukraine 182 National Technical University of Athens (NTUA), Athens, Greece 183 Naturhistorisches Museum Wien (NHM), Vienna, Austria 184 Niels Bohr Institute, Copenhagen University (NBI), Copenhagen, Denmark 185 Nigde Ömer Halisdemir University (OHU), Nigde, Turkey 186 Northern Illinois University (NIU), DeKalb, IL, USA 187 Northwestern University (NU), Evanston, IL, USA 188 Novosibirsk State University (NSU), Novosibirsk, Russia 189 Otto-von-Guericke-Universityät Magdeburg (OVGU), Magdeburg, Germany 190 Oxford University (UOXF), Oxford, UK 191 Paul Scherrer Institute (PSI), Villigen, Switzerland 192 Peking University (PU), Beijing, P.R. China 193 Perimeter Institute for Theoretical Physics (PI), Watterloo, Canada 194Petersburg Nuclear Physics Institute, NRC "Kurchatov Institute" (PNPI), Gatchina, Russia 195 Piri Reis University (PRU), Istanbul, Turkey 196Pittsburgh Particle physics, Astrophysics & Cosmology Center and Department of Physics & Astronomy, University of Pittsburgh (PITT PACC), Pittsburgh, PA, USA 197 Princeton University (PU), Princeton, NJ, USA 198PRISMA Cluster of Excellence, Inst. für Physik, Johannes-Gutenberg-Universität (PRISMA), Mainz, Germany 199 Pusan National University (PNU), Busan, Republic of Korea 200 Queen's University (Queens U), Kingston, Canada 201 RAMENTOR Oy (RAMENTOR), Tampere, Finland 202 Rheinisch-Westfälische Technische Hochschule Aachen (RWTH), Aachen, Germany 203 Riga Technical University (RTU), Riga, Latvia 204 Royal Holloway University (RHUL), London, UK 205 Ruder Boskovic Institute (RBI), Zagreb, Croatia 206 Ruprecht Karls Universität Heidelberg (RKU), Heidelberg, Germany 207 Rutgers, The State University of New Jersey (RU), Piscataway, NJ, USA 208 Sapienza Università di Roma (UNIROMA1), Rome, Italy 209School of Particles and Accelerators, Institute for Research in Fundamental Sciences (IPM), Tehran, Iran 210 School of Physics and Astronomy, University of Glasgow (SUPA), Glasgow, UK 211Science and Technology Facilities Council, Daresbury Laboratory (STFC DL), Warrington, UK 212Science and Technology Facilities Council, Appleton Laboratory (STFC RAL), Rutherford, Didcot, UK 213 scMetrology SARL (scMetrology), Geneva, Switzerland 214 Scuola Int. Superiore di Studi Avanzati di Trieste (SISSA), Trieste, Italy 215 Scuola Normale Superiore (SNS), Pisa, Italy 216 Seoul National University (SNU), Seoul, Republic of Korea 217 Sevaplan und Wurm Schweiz AG (WURM), Winterthur, Switzerland 218 Shahid Beheshti University (SBUT), Tehran, Iran 219 Shanghai Jiao Tong University (SJTU), Shanghai, P.R. China 220 Shirokuma GmbH (Shirokuma), Wetzikon, Switzerland 221Skobeltsyn Institute of Nuclear Physics, Lomonosov Moscow State University (SINP MSU), Moscow, Russia 222 Southern Federal University (SFU), Rostov-on-Don, Russia 223 Southern Methodist University (SMU), Dallas, TX, USA 224Sri Guru Tegh Bahadur Khalsa College, University of Delhi (SGTB Khalsa College), New Delhi, India 225 Stanford National Accelerator Center (SLAC), Menlo Park, CA, USA 226 Stanford University (SU), Stanford, CA, USA 227 Stony Brook University (SBU), Stony Brook, NY, USA 228 Technische Universität Darmstadt (TU Darmstadt), Darmstadt, Germany 229 Technische Universität Dortmund (TU Dortmund), Dortmund, Germany 230 Technische Universität Dresden (TU Dresden), Dresden, Germany 231 Technische Universität Graz (TU Graz), Graz, Austria 232 Technische Universität Wien (TU Wien), Vienna, Austria 233 Tel Aviv University (TAU), Tel Aviv, Israel 234 The Citadel, The Military College of South Carolina (Citadel), Charleston, SC, USA 235 The Pennsylvania State University (PSU), University Park, PA, USA 236 The University of Tokyo (Todai), Tokyo, Japan 237 Thomas Jefferson National Accelerator Facility (JLab), Newport News, VA, USA 238 TOBB University of Economics and Technology (TOBB ETU), Ankara, Turkey 239 Tokyo Institute of Technology (Tokyo Tech), Tokyo, Japan 240 Trinity College Dublin (TCD), Dublin, Ireland 241 Tri-University Meson Facility (TRIUMF), Vancouver, Canada 242 Tsinghua University (THU), Beijing, P.R. China 243 Tsung-Dao Lee Institute (TDLI), Shanghai, P.R. China 244 Uludag University (ULUÜ), Bursa, Turkey 245 Universidad Autónoma de Sinaloa (UAS), Culiacán, Mexico 246 Universidad de Guanajuato (UGTO), Guanajuato, Mexico 247 Universidad de La Laguna (ULL), La Laguna, Spain 248 Universidad de la República (Udelar), Montevideo, Uruguay 249 Universidad de los Andes (Uniandes), Bogotá, Colombia 250 Universidade de São Paulo (USP), São Paulo, Brazil 251 Universidade do Estado do Rio de Janeiro (UERJ), Rio de Janeiro, Brazil -- 252 Universidade Federal de Pelotas (UFPel), Pelotas, Brazil 253 Universidade Federal de Rio de Janeiro (UFRJ), Rio de Janeiro, Brazil 254Università degli Studi Roma Tre – Centro Ricerche Economiche e Sociali Manlio Rossi-Doria (EDIRC), Rome, Italy 255 Università della Calabria (UNICAL), Arcavacata, Italy 256 Università del Salento (UNISALENTO), Lecce, Italy 257 Università di Bari (UNIBA), Bari, Italy 258 Università di Bologna (UNIBO), Bologna, Italy 259 Università di Cagliari (UNICA), Cagliari, Italy 260 Università di Catania (UNICT), Catania, Italy 261 Università di Ferrara (UNIFE), Ferrara, Italy 262 Università di Firenze (UNIFI), Florence, Italy 263 Università di Genova (UNIGE), Genoa, Italy 264 Università di Insubria (UNINSUBRIA), Milan, Italy 265 Università di Lecce(UNILE), Lecce, Italy 266 Università di Milano (UNIMI), Milan, Italy 267 Università di Padova (UNIPD), Padua, Italy 268 Università di Parma (UNIPR), Parma, Italy 269 Università di Pavia (UNIPV), Pavia, Italy 270 Università di Perugia (UNIPG), Perugia, Italy 271 Università di Roma Sapienza (UNIROMA1), Rome, Italy 272 Università di Roma Tor Vergata (UNIROMA2), Rome, Italy 273 Università di Roma Tre (UNIROMA3), Rome, Italy 274 Università di Torino (UNITO), Turin, Italy 275 Università di Udine (UNIUD), Udine, Italy 276 Universität Hamburg (UHH), Hamburg, Germany 277 Universität Heidelberg (HEI), Heidelberg, Germany 278 Universitat Politecnica de Catalunya (UPC), Barcelona, Spain 279 Universität Siegen (U Siegen), Siegen, Germany 280 Universität Tübingen (TU), Tübingen, Germany 281 UniversitéClermont Auvergne (UCA), Aubière, France 282 UniversitéGrenoble Alpes (UGA), Grenoble, France 283 University College London (UCL), London, UK 284 University of Applied Sciences Technikum Wien (UAS TW), Vienna, Austria 285 University of Arizona (UA), Tucson, AZ, USA 286 University of Basel(UNIBAS), Basel, Switzerland 287 University of Belgrade (UB), Belgrade, Serbia 288 University of Bergen (UiB), Bergen, Norway 289 University of Bern (UNIBE), Bern, Switzerland 290 University of Birmingham (UBIRM), Birmingham, UK 291 University of Bristol (UOB), Bristol, UK 292 University of California Berkeley (UCB), Berkeley, CA, USA 293 Davis (UCD), University of California, Davis, CA, USA 294 Irvine (UCI), University of California, Irvine, CA, USA 295 San Diego (UCSD), University of California, San Diego, CA, USA 296 University of California Santa Barbara (UCSB), Santa Barbara, CA, USA 297 University of California Santa Cruz (UCSC), Santa Cruz, CA, USA 298 University of Cambridge (CAM), Cambridge, UK 299 University of Chicago (UCHI), Chicago, IL, USA 300 University of Cincinnati (UC), Cincinnati, OH, USA 301 University of Edinburgh (ED), Edinburgh, UK 302 University of Florida (UF), Gainesville, FL, USA 303 University of Geneva (UniGE), Geneva, Switzerland 304 University of Illinois at Urbana Champaign (UIUC), Urbana Champaign, IL, USA 305 University of Iowa (UIowa), Iowa City, IA, USA -- The Auvergne-Rhône-Alpes regional government is headed by a prefect who is supported by an office (Secrétariat Général de la Région Auvergne-Rhône-Alpes, SGAR) located in Lyon. Within this administration, the prefect is the representative of the French Republic. The SGAR and the prefect's office work together on all development activities in the area. In 2016 the SGAR launched an analysis so that the prefect, and in turn the French national administration, could be informed about a significant extension of CERN's infrastructure and to estimate the associated administrative and financial impacts for France. This activity led to the establishment of a series of regular meetings with CERN for the development of the preparatory phase. France promotes a "participative democracy" [549–551], calling for a process to find a consensus through open discussions amongst all stakeholders in the project from the conceptual stage onwards. The process starts with the development of the basic concept, a feasibility study concerning the infrastructural challenges, a proposal for the governance and funding and a socio-economic cost-benefit analysis. The infrastructural changes concern a wide range of topics: the use of excavation material, a concept for managing conventional waste during all project phases, an energy management plan that can be integrated with the territorial energy balance plan, plans for the consumption of resources such as water, proposals for synergies with the host state to contribute to the territorial development, the development of traffic and mobility concepts and further topics. CEREMA6, a public entity associated with the ministry of ecological transition and solidarity and the ministry of territorial cohesion, has produced a report for the SGAR and the prefect on the impact of an FCC for the host state concerning administrative processes and the associated financial engagements [552]. -- MVDC distribution systems are an active area of academic research that spans various sectors including electrical engineering, electronics, information and computing technologies, reliability engineering, functional safety, economics and business analysis. Consequently, this is an ideal application to bring academic partners with complementary competencies from different geographical regions together at CERN in a concrete technological research project with tangible impact potential at academic levels, with high-educational value and with opportunities to work in a close-to-market environment. Specifically, EPFL (Lausanne, Switzerland), a technical university, has an active programme on the development of MVDC power distribution networks with support from the Swiss Federal Office of Energy (SFOE). -- The research, which led to this publication has received funding from the European Union's Horizon 2020 research and innovation programme under the grant numbers 654305 (EuroCirCol), 764879 (EASITrain), 730871 (ARIES), 777563 (RI-Paths) and from FP7 under grant number 312453 (EuCARD-2). The information herein only reflects the views of its authors. The European Commission is not responsible for any use that may be made of the information. Trademark notice: All trademarks appearing in this report are acknowledged as such. -- Emittance The area in phase space occupied by a particle beam. The units are mm-milliradians for transverse emittance and eV·s for longitudinal emittance. EN European norms are documents that have been ratified by one of the three ESOs (European Standardisation Organisations), CEN, CENELEC or ETSI; recognised as competent in the area of voluntary technical standardisation as for the EU Regulation 1025/2012. EOT The most common type of overhead crane, found in many factories. These cranes are electrically operated by a control or remote control pendant, or from an operator cabin attached to the crane. EPFL The École polytechnique fédérale de Lausanne is one of the two Swiss Federal Institutes of Technology. EPPSU European Particle Physics Strategy Update. See also https:// europeanstrategy.cern. ERL Energy recovery Linac. ERMC Enhanced racetrack model coil. ES Electro static. ESD Electron-stimulated desorption. ESFRI European strategy forum for research infrastructures. Espoo Convention The Espoo Convention sets out the obligations of parties to assess the environmental impact of certain activities at an early stage of planning. It also lays down the general obligation of states to notify and consult each other on all major projects under consideration that are likely to have a significant adverse environmental impact across boundaries. ESPP European Strategy for Particle Physics. See also https:// europeanstrategy.cern. ESRF The European Synchrotron Radiation Facility is a joint research facility sit-uated in Grenoble, France, and supported by 22 countries (13 member coun-tries: France, Germany, Italy, UK, Spain, Switzerland, Belgium, The Netherlands, Denmark, Finland, Norway, Sweden, Russia and 9 associate countries: Austria, Portugal, Israel, Poland, Czech Republic, Hungary, Slovakia, India and South Africa). ESS Energy storage system. ETHZ The Eidgenössische Technische Hochschule Zürich is one of the two Swiss Federal Institutes of Technology. EU European Union. EuCARD2 A FP7 EC funded research and development project in the area of particle accelerator technologies. EuroCirCol A H2020 EC funded research and development project to develop the foundations of a future circular hadron collider. EW Electroweak. EWPO Electroweak precision observables. EWPT Electroweak phase transition. EWSB Electroweak symmetry breaking. EXP Experiment. Experiment insertion region Place in the particle collider hosting the interac-tion region in which the two beams are brought to collision and the surrounding particle physics experiments. EXT Extraction.