The First Nations of Canada have been active over the past three decades in negotiating natural resources co-management arrangements that would give them greater involvement in decisionmaking processes that are closer to their values and worldviews. These values and worldviews are part of the traditional ecological knowledge (TEK) that First Nations possess about the land; to reach agreements to the satisfaction of First Nations, appropriate ways to involve TEK in decision-making processes must be designed. Through a review of the literature on TEK, I identified six “faces” of TEK, i.e., factual observations, management systems, past and current land uses, ethics and values, culture and identity, and cosmology, as well as the particular challenges and opportunities that each face poses to the co-management of natural resources.