Complex multistrata agroforestry systems (CMSAFs) are tree-dominated land use systems with two or more strata of trees or shrubs and a substantial degree of structural complexity within at least one of the strata. They cover several million hectares in the tropics. This article distinguishes: (1) CMSAF based on understorey tree crops; (2) CMSAF based on overstorey tree crops; (3) intensively managed mixed systems such as homegardens; and (4) forest-enrichment systems. It discusses their ecology, distribution, dynamics, environmental functions, productivity, and possibilities for improvement of their profitability. In view of current pressures to intensify tropical land use systems, CMSAF have the best prospects to remain part of the landscape in areas where there are specific government policies for conserving them, such as in inhabited protected areas.