Should it be permissible to launch a citizens` initiative demanding the reintroduction of the death penalty? May a proposal be put to a popular vote despite the fact that voters are not properly informed about its effects? Should the people be allowed to vote on the adoption of immigration restrictions that violate international law? With the mushrooming of direct-democratic instruments throughout Europe and the introduction of the European Citizens` Initiative (ECI), the relationship between popular sovereignty and the rule of law is set to become one of the defining political issues of our time. Where should the legal limits of direct democracy be drawn? Who should review compliance with these limits? It is the objective of LIDD to provide the scientific basis for answering these questions. The project builds on a comparative legal analysis, making it possible to capitalize on the wealth of experience gained with direct-democratic instruments in Switzerland and, more recently, other European states in order to develop general conclusions.