Abstract Forest structure and composition are central to understanding how forest ecosystem’s function, respond to disturbance and store carbon. Structural attributes such as diameter at breast height (DBH), tree height, stem density and basal area, together with species composition, diversity indices and vertical stratification, provide an integrated picture of stand development and ecological processes. This narrative review synthesizes key concepts and metrics of forest structure and composition, with emphasis on: (1) stand structure (DBH, height, density, basal area); (2) species composition and diversity indices (Shannon, Simpson); (3) vertical stratification across canopy, understory and ground layers; (4) age/size class distributions; and (5) forest succession pathways. It then illustrates these concepts using examples from evergreen, semi-evergreen and deciduous forests in Ratanakiri and Mondulkiri Provinces, Cambodia, where dry evergreen and deciduous dipterocarp forests form extensive landscapes and are increasingly targeted for conservation and REDD+ initiatives. Forest structure in these landscapes is shaped by gradients in soil moisture, fire regime and land-use history, leading to distinct patterns of basal area, stem density and diversity among forest types. Understanding these structural patterns is essential for designing sampling protocols, modelling carbon stocks and planning forest management in Cambodia and across tropical Southeast Asia. Keywords: forest structure, species composition, Shannon index, Simpson index, vertical stratification, forest succession, evergreen forest, deciduous dipterocarp, Cambodia.