Religious diversity has significant consequences on the urban environment, and primarily because of the new spaces that it entails. These spaces engender complex problems of regulation, including specific issues related to urban planning. This article will mainly consider the current situation in Italy. Its focus will be on the region of Lombardy, in northern Italy, and on the newly-introduced regulations governing the construction and location of minority places of worship (and of mosques in particular). The example of the region’s planning policies and regulations offers an opportunity for a critical rethinking of certain fundamental issues related to urban planning for multiculturalism and diversity. In this perspective, the article stresses the importance of focusing also on the role of planning and building rules and laws in order to protect and promote (religious) diversity and pluralism.