This thesis develops and tests a model of political representation based on the participation and specialisation decisions of individual MEPs. Political representation is determined by the institutional and party-political incentives that guide legislative behaviour at different stages of the policy process. Proportionality requirements, majority rule and intra-party politics affect whether MEPs engage in different legislative activities in the European Parliament and the extent to which they specialise in the policy areas that their national party stands for. The model can be adapted to a wide range of legislative activities and to different institutional environments. At the decision-making stage, majority rule makes participation most attractive to MEPs from party groups that are pivotal under the majority thresholds required to pass legislation. In contrast, minority MEPs limit their participation to the policy areas that are salient to their national party. In other words, minority legislators are more responsive than majority MEPs. In policy formulation, an auction system enforces a proportional allocation of committee reports, which favours the representation of a broad range of values and interests across the political spectrum. However, competition among party groups affects who gets the most desirable reports. Open rule enforces a distribution of salient reports in line with voting coalitions in the plenary and on the committee floor. Within party groups, the leadership distributes reports in an effort to maintain group cohesion. As a result, majority legislators who are loyal to their party groups are more responsive than other MEPs. Finally, in parliamentary oversight at Question-Time, party groups do not have any gate-keeping powers. Also, national parties rather than party groups are the primary actors in legislative-executive relations. MEPs without national party ties to the Commission attribute a greater role to overseeing the executive in a large range of policy areas than 'governing' MEPs. As a result, such 'opposition' MEPs are better represented at this stage of the policy process but they specialise less in salient policy areas.