This work discusses questions on political participation, representation and legitimacy in the European Union national parliaments. Three major empirical questions structure the book: What affects women's presence in parliaments?, Does the number of women in parliament have an effect? And are women in parliament representing women? Empirical evidences show that institutional reforms need a 'minimal environment' in terms of socio-economic development so as to prove effective. As opposed to the critical mass theory, claiming that a few representatives cannot have an impact on the political outcomes, here the empirical evidences suggest that smaller groups can also influence the different components of the legislative process. The last part turns to the fundamental question of whether a parliament that is descriptively representative, i.e. in which the parliamentarians share certain characteristics with the voters, also is a substantively descriptive parliament, i.e. in which the parliamentarians mirror the voters' opinions.