This contribution studies the different preferences of Moroccan Islamists and leftists for cooperating with each other. The Islamist Party of Justice and Development (PJD) has been actively seeking an alliance with the leftist Socialist Union of Popular Forces (USFP) since 2007. The USFP’s national leadership has avoided any form of cooperation with the Islamists at the national level, but had to tolerate government coalitions at the local level. We find that the most important driver behind the USFP’s reluctance to ally with the Islamists is its co-optation. The asymmetry in electoral strength and differences in the type of electoral support the two parties enjoy also appear to be important reasons behind the different party preferences. For the PJD, its superior electoral support and the higher degree of programmatic support it enjoys suggest that it expects to be successful in democratic elections, while the opposite seems to be the case for the USFP. Ideology, by contrast, was found to be of little importance in determining the positions of the national PJD or USFP leadership towards cross-party cooperation. The analysis is based on original field research conducted in Morocco and on data from the World Values Survey.