A definitive single hypothesis about HIV pathogenesis is still lacking in specialized literature. Rather, a picture of the extreme complexity in AIDS causality ensues from the extensive information available. This article contains an outline of the most relevant data on the subject of AIDS pathogenesis, organized into genetic, molecular, cellular, immunological and physiological levels. This scheme shows how events triggered by HIV, together with virus and host factors, compose a network whose interacting components define the heterogeneity of disease manifestations and which redefine the necessity of considering multiple approaches to therapy and vaccine design.