Koa (Acacia koa) is a tree species endemic to Hawaii that is of immense ecological and economic importance. This species has been mined from local forests for its wood for more than 100 years, and extensive areas of koa-dominated forests have been converted to grazing lands. Today, in recognition of the great importance and value of koa and the forests in which it is found, there is substantial interest in restoration and management of koa forests. This report brings together knowledge on the biogeography, physiology, ecology, and silviculture of koa in an effort to assist landowners and resource stewards in making sound decisions about restoring and managing koa forests.