The Atlas of breeding birds of Portugal makes an inventory of all 235 breeding species, from which 221 are native species, and 205 presenting a regular breeding activity. The Atlas covers a period from 1999 to 2005. The project "Atlas of breeding Birds of Portugal" aimed to know the current distribution of breeding species in Continental Portugal and in the autonomous regions of Madeira and the Azores. It pretended also to characterize the abundance, when possible, of national populations of these species, during the period of 1999 to 2005. This dataset comprised two layers of information: Directed Census - Distribution data of birds target-species by directed census, except for Aquila adalberti, Aegypius monachus and Pterocles alchata whose location is confidential (includes marginal 10x10 km UTM grids); Other species - distribution data for the remaining species (excluding UTM 10x10 km marginal grids). The project involved the participation of ca. 500 volunteers, more than a dozen professional collaborators and various working teams. The project results from a fundamental partnership with three other entities, namely the SPEA – Sociedade Portuguesa para o Estudo das Aves (Portuguese Society for the Study of Birds, a non-governmental association that works for the conservation of birds and their habitats in Portugal and which brings together numerous members interested in this faunal group); the Parque Natural da Madeira (PNM, Madeira Natural Park), and the Direção Regional do Ambiente dos Açores (DRA, Regional Environment Directorate of the Azores), entities responsible for the conservation of wild birds in the autonomous regions. The Atlas contains occurrence data for breeding birds belonging to 20 orders, 58 families, 115 genus, and 180 species.