In line with the Urban Agenda for the EU, this article highlights the importance of local actions in the conservation of biodiversity, both through specific activities and by increasing the availability of information. As such, the policies and projects related to the conservation of biodiversity have been analyzed here at different levels and, in particular, the initiatives undertaken in the Madrid Region, Spain. Consequently, two cases are presented that demonstrate the role that local administrations can play in improving the biodiversity database, and hence, in the effective protection of areas of significant environmental value. First, we will examine the effects that creating an environmental inventory of vegetation, flora and landscape has had in Torrelodones. Second, among the more recent environmental policies implemented in the municipality of Madrid are those that resulted in the environmental recovery of the urban section of the Manzanares River. Both these actions demonstrate how local authorities can contribute to the conservation of biodiversity at relatively low expense and in line with EU guidelines. Notably, this occurred despite the fact that competences in environmental matters in Spain are not municipal. In this context, the paper reflects on the untapped potential of the General Urban Planning Plans (PGOU) in deep knowledge and sustainable and responsible management of municipal environmental values.