The aim of the thesis is to investigate how service in the European Parliament (EP) between 2004 and 2009 influenced the attitudes, identities and behaviour of the Polish members of the chamber. The study of the Polish contingent is carried out with a view to contributing to discussions of the phenomenon usually referred to as the "socialisation" of Members of the European Parliament (MEPs). For the purposes of the present analysis, three aspects of socialisation are differentiated: institutional learning (MEPs learning to participate effectively in the work of the chamber), adaptation to the institutional culture of the EP (MEPs discovering the norms and codes of conduct characteristic for the EP) and attitude change (evolution of political views as a result of contacts with other MEPs).