The main goal of this paper is to identify and test the principal institutional determinants of the power capacities that actors hold in the EP´s policy-making. By determinants we mean the (institutional) factors as well as the conditions under which actors become powerful in the development of the EP´s legislative process. So far in relation to institutional sources of power, rapporteurs and shadow rapporteurs have received much attention in the literature (Yordanova 2010; Costello and Thomson 2010; Ringe 2010; Finge 2012). There is a general agreement that those actors are frequently ´powerful` actors. However, we do not know the extent to which they are powerful (in relation to other actors) as well as the conditions under which they are ´powerful`. On the other hand, the influence of committee chairs and group leaders has received little or no attention. Thus, the point of departure of this research will start where those ´findings` of the literature have ended. Thus, the research question we pose is: Under what conditions rapporteurs, shadow rapporteurs, committee chairs and group leaders can explain variation of their formal (and informal) power in EP legislative decision-making? In order to do so, this research will collect a unique data set that ´measures` the (formal and informal) capacities of EP key actors both in a systematic way (by using quantitative scales) as well as in a number of case studies that help to identify conditions under which those actors become more (or less) relevant institutional actors
