The article focuses one of the most delicate theoretical issues of liberal and democratic constitutionalism: political representation and limits to party switching. On the one hand, the principle of "free parliamentary mandate" seems to preclude the possibility to introduce limits to the party switching, on the other hand the substantial compliance with the will of the voters and the principle of popular sovereignty seem to call for provisions as to disqualification of a member of Parliament or of other Legislature on the ground of defection from his political party. Between the large number of States that have adopted anti-defection laws over the past several decades, the article focuses the nature and the effects of such laws in Brasil, India, South Africa and Portugal. The party mandate as anti-defection measures is compatible with democratic State, but there is no valid response in absolute as to whether its introduction is a sign of democratic progress or regression. While it is almost completely absent in old democracies, in new democracies anti defection law seems to play an important role to tackle political corruption. The adoption of anti-defection laws has a strong impact on party system and requires other measures to ensure democratic process within each political party.