Research on constitutional law has come in different waves mirroring the development of states in recent decades. While the decolonization period of the 1960s still kept the old ties of constitutional "families," comparison based on such ties has become ever less persuasive since the 1980s wave of constitution making following the fall of the Berlin Wall. Research about de facto and de jure constitutional law now tends to embrace institutional details like judicial review powers and procedures of direct democracy. The field of comparative constitutional law is controversial both in methods and substance. It still lacks a consistent framework of comparative tools and is criticized as illegitimate by scholars who insist on the interpretive autonomy within each constitutional system.Research in the area of fundamental rights has to deal with long-lasting controversies like the constitutionality of the death penalty. Bioethical regulation is another new field where constitutional positions tend to diverge rather than converge. Embryonic stem cell research, therapeutic cloning, pre-implantation genetic diagnosis, and surrogate motherhood are examples from biotechnology and reproductive medicine where constitutional scholars disagree about what, if anything, constitutional law can contribute to provide a basis or limit for regulation. With the worldwide rise of constitutional courts and judicial review, the standards for the interpretation of fundamental rights become more important. Legal scholarship has worked out the differences between the rule-oriented approach associated with Anglo-American legal systems versus the principle-based approach common to continental Europe.