The referendum constitutes one of the oldest forms of decision-making by citizens. By being a direct expression of the will of citizens, in nowadays democracies, it is rarely used. However, referendum takes a special importance in questions of bigger relevance for the citizens or nations. Such cases are those of territorial problematics, and the constitutional referendum for approval or change of constitutions. There are lots of forms of direct democracy, except for the referendum; there are also the plebiscite, the popular legislative initiative, the electors gatherings. This paper highlights the importance of the referendum on constitutional provisions of different countries and its difference with the other forms of direct democracy. Another novelty of this paper constitutes the treating of some new opportunities given to the European citizens by the Lisbon Treaty, as possibilities for the citizens to take part in the decision-making process. Such possibilities are citizen initiatives, dialogue with representative associations and civil society, as well as an open and transparent dialogue with churches, associations and religious communities of the member states.