Avian malaria is the oldest experimental system for investigating the biology and transmission of Plasmodium parasites. Recent molecular protocols for detecting and characterizing avian malaria lineages in the field are providing an ever-growing picture of the prevalence, distribution, host range, and diversity hotspots of avian malaria across the world. The unparalleled genetic diversity uncovered rivals anything that has been found in other vertebrate malarias and seems to be matched by an equally rich phenotypic diversity, providing endless opportunities for exploring the selective pressures under which hosts and parasites evolve. We review the most important milestones in avian Plasmodium research and explain why this is a unique animal model to understand the ecology and evolution of malaria. Avian malaria is the oldest experimental system for investigating the biology and transmission of Plasmodium parasites. Avian Plasmodium has been found infecting thousands of bird species in all geographic regions except Antarctica. Its prevalence and genetic diversity rivals anything that has been found in any other vertebrate malaria. Several avian Plasmodium lineages and their most common natural vector, the mosquito Culex pipiens, are widespread and easy to maintain in the laboratory – meaning that the system is also easily amenable to laboratory experiments. The unparalleled genetic diversity of avian malaria uncovered thus far is likely matched by an equally rich phenotypic diversity, providing a unique opportunity for exploring the selective pressures under which hosts and parasites evolve. This will be best achieved by combining empirical and experimental studies in the field, with experimental infections in controlled laboratory conditions.