The age structure of a stand provides an understanding of important ecological processes taking place during stand development. The age of trees has been estimated by historical records, estimation from tree size, ring counting at breast height and ground level, pith node counting, and dendrochronological cross dating. Each of these methods has inherent advantages and limitations. In the fire-driven boreal forest, stand age structure has been found to shift from a relatively even-aged structure, where all trees establish immediately after fire with a similar height and diameter, to one that is uneven-aged, where trees vary in height and diameter as time since fire increases. The age structure dynamics differ with stand species composition and influenced by non-stand replacing disturbances. Traditional forest management can shift the age structure at both the stand and landscape level, but silvicultural systems and forest management planning techniques are available to mimic natural age structural patterns.