An important but challenging development appears to be occurring in the character of some constitutional courts—a shift from their traditional role as a negative legislator to a significant role as a positive legislator. Under this shift, a constitutional court is no longer confined to declaring the unconstitutionality of statutes if they are contrary to the constitution and simply annulling them, but rather takes on a positive power to create statute law. The case study examined here is the power to fill the gaps caused by unconstitutional legislative omissions (ULOs). Such a power authorises a constitutional court to declare what a missing law should contain, and to draft and promulgate that law, thus assuming the role of positive legislators by enacting temporary or provisional rules on specific matters. This development in the power of constitutional courts provokes vital questions. Why has such a role developed? What are its most important manifestations? What are the benefits and risks of such powers? Do the benefits outweigh the risks, and how might benefits be maximised and risks minimised? In response to these questions, this study provides a deeper understanding of the apparent shift in constitutional courts’ power from negative to positive legislator, and its implications for countries struggling with establishment and maintenance of democracy. The study applies lessons from international experience of powers to rectify ULOs in 17 countries, to examine whether such powers help address these challenges in more legal systems, and if so, how. It finds that some forms of such a power do have a positive contribution to make in response to serious constitutional challenges, but two things are required: a general recognition that the traditional understanding of a constitutional court as a purely negative legislator is no longer sufficient to explain and evaluate its role, once entrusted with such a power; and a new approach to the design of such a power, such as developed and applied in this thesis, which enables this ‘positive legislator’ role to be granted in a manner that still protects core values of liberal democracy.