This dissertation examines local government policy-making on policies that concern Muslim immigrants and their descendants in Western Europe.Governments across the region struggle to integrate these populations economically, socially, and politically, even though large-scale Muslim immigration began after World War Two.We would expect center-left political parties to promote Muslim interests and drive integration efforts because these parties are socially liberal, and have historically represented minorities and individuals with low socioeconomic status.Contrary to these expectations, I show that there is great variability in center-left policies towards Muslims and minorities more generally.Using a unique dataset of more than 750 policies that I constructed using meeting records from district governments in Berlin, Germany, I demonstrate that center-left parties set the agenda on the incorporation of Muslims in some locations, but are largely absent from integration policy-making in other parts of the city.This finding contrasts the dominant notion in the immigration literature that European center-left parties consistently advocate for Muslims and minorities.It is difficult to predict where center-left parties will be active on immigrant policy issues because party behavior differs in demographically and institutionally similar districts.Center-left policy-making even varies in districts with comparably sizable immigrant populations.Inconsistencies in party behavior generate the central question I explore in my dissertation:Why do the same center-left parties endorse immigrant interests in some locations and not in others? To explain deviations in center-left behavior, I first turn to sociological and institutional theories of party behavior.However, my data show that neither demographics nor institutions account for this variance.Center-left politicians are not more active on integration in districts with large numbers of immigrants or where their party controls government.Given that these factors cannot explain party behavior on integration, I offer an alternative approach that emphasizes local-level political party competition.I argue that strategic electoral concerns affect center-left policy-making, and that these interests supersede demographics, institutions, and even underlying policy demand.Electoral competition is an important concern for European center-left parties because their working class base has deteriorated and competition from far-right and far-left parties for traditional center-left constituencies has intensified.