Backed by a prescribed amount of signatures, a citizens’ initiative is a petition calling for a referendum on a legal proposal drafted by the citizens. The actual referendum is the second step. In an obligatory referendum certain issues must be put before the citizens for approval (for example amendments to the constitution or membership in an international organization).
Direct democracy must follow fair and transparent rules, and must not be limited by quorums or any other barriers.
Democracy International's agenda complies with the "Code of Good Practice on referenda“ published by the Venice Commission, which sets out fair criteria for direct democracy. The Venice Commission was established by the Council of Europe to give advice to states on constitutional questions, and the Code draws upon the European electoral heritage of universal, equal, free and secret suffrage.
The Venice Commission defines conditions for the implementation of these principles plus specific rules that should regulate the embodiment of referenda, including "respect for fundamental rights“, the "observation of the referendum“ and the existence of an effective system of appeal“. You can find more Information in the "Code of Good Practice on Referenda".
Professor Matt Qvortrup of the University of Coventry has published a Bibliography on Direct Democracy and Referendums, you can download it here.
More information: "What’s a people’s or citizens’ initiative?", Film by Michele Andina, swissinfo.ch