This study analyzes the processes leading to the presence or absence of opposition to mosque construction in Spain. Specifically, it seeks to explain why there has been such strong opposition to mosque construction in the northeast region of Catalunya relative to other regions. I examine this question through four in-depth case studies, two of which concern recent failed attempts to establish mosques in 'the province of Barcelona, Catalunya, and two of which concern recent successes with establishing mosques in the province of Malaga, Andalucia. I utilize semi-structured interviews and written materials to gather data on these cases, and I employ discourse and relational analyses to explain the variation in outcomes in my settings of focus. Discourse analysis allows me to illuminate the dominant categories and tropes that characterize mosque debates, while relational analysis allows me to situate such debates within the broader social contexts and institutional matrices in which they operate. I also plan to .devote specific attention to how public debates have shifted with key events, such as the Madrid bombings, which have altered current understandings of mosques, and Muslim presence more generally. This study makes an important contribution to our understanding of the integration of Muslims in Spain, and in Europe more generally, as well as broader debates on multiculturalism, immigrant incorporation, and the construction and maintenance of symbolic boundaries.