Deliberative democracy theory suggests that wide and open public discourse is a way to overcome legitimacy crisis in the modern world. Jürgen Habermas maintains that modern society conceives a law as institutionalisation of practical discourse on social norms. National parliaments are among the main institutional contexts for deliberations in representative democracy and parliamentary discourse is said to be the core of Western democracy. Although some theorists question the influence of parliaments on the results of political process as in many cases they only ratify decisions made by the executive, other scholars emphasise their legitimating function. However, recent public opinion surveys in some European countries indicate very low public trust rates of national parliaments which possibly is a reflection of perceived poor political performance. Attitudes towards the democratic institutions and system can also be used as measures of democratic legitimacy. This article analyses how parliamentary decision-making and legitimacy (and trust) are interconnected – a hypothesis to be proved in the future.