Caribou (Rangifer tarandus) is a species of deer that lives in the tundra, taiga, and forest habitats at high latitudes in the northern hemisphere, including areas of Russia and Scandinavia, the United States, and Canada. Caribou is the species’ common name in North America, while reindeer is used in Europe and Asia. Woodland caribou (Rangifer tarandus caribou), a subspecies of caribou, has been listed under the Canadian Species at Risk Act (SARA) as threatened. Six populations of woodland caribou are recognized in Canada, where three have a conservation status of endangered (Southern Mountain, Central Mountain, and Atlantic-Gaspésie), one threatened (boreal), and two special concern (Northern Mountain and Newfoundland). Many of the populations across the species range are experiencing range retraction and population declines, believed to be predominately driven by unsustainable predation that is facilitated through habitat alteration (i.e., habitat loss, degradation, and fragmentation). Additional threats contributing to the decline or that may serve to impede recovery of woodland caribou have been identified: range encroachment by other ungulates species (i.e., moose and deer); disease and parasites; forage and nutritional limitations; and climate change. These individually and cumulatively have been documented in contributing to the decline of the species. Current population estimates and trends for a significant portion of woodland caribou subpopulations remain unknown because of absence or infrequency of monitoring, making it especially challenging to attribute cause and effect of declines. Although the magnitude of scientific research undertaken to date to better understand this species is substantial, it remains incomplete in several key research areas. While significant efforts have been made to understand the species’ basic ecology and predator-prey dynamics, topics associated with genetics, nutrition, parasites, and diseases remain understudied across the species range, inhibiting effective management and recovery efforts for the species. Here, NCASI synthesizes current scientific literature to describe the state-of-knowledge of woodland caribou and conduct a gap analysis for the most recent decade (2009 to 2019) of research to assist the future direction of research and to identify knowledge and information gaps on woodland caribou.