Białowieża Forest is a forest on the border between Belarus and Poland. It is one of the last and largest remaining parts of the immense primeval forest that once stretched across the European Plain. The forest is home to 800 European bison, Europe's heaviest land animal. UNESCO's Man and the Biosphere Programme designated the Polish Biosphere Reserve Białowieża in 1976 and the Belarusian Biosphere Reserve Biełavieskaja pušča in 1993.

An old-growth forest is a forest that has developed over a long period of time without disturbance. Due to this, old-growth forests exhibit unique ecological features. The Food and Agriculture Organization of the United Nations defines primary forests as naturally regenerated forests of native tree species where there are no clearly visible indications of human activity and the ecological processes are not significantly disturbed. One-third of the world's forests are primary forests. Old-growth features include diverse tree-related structures that provide diverse wildlife habitats that increases the biodiversity of the forested ecosystem. Virgin or first-growth forests are old-growth forests that have never been logged. The concept of diverse tree structure includes multi-layered canopies and canopy gaps, greatly varying tree heights and diameters, and diverse tree species and classes and sizes of woody debris.