Tacit knowledge is a generally unarticulated, preconscious form of knowledge that forms a basis for human judgment and decision making. Tacit knowledge is acquired primarily through experience, usually observation of and working with "qualified" teachers or mentors. Tacit knowledge may also be described as "practical," that is, derived from experience or practice, and "taken-for-granted." It involves either skill (the ability to do something well) or perceptual ability (gaining knowledge through the senses that would not be obvious to an inexperienced person). It generally requires a background of knowledge or a theoretical (conceptual) framework as a context for understanding. Decisions based on tacit knowledge can be articulated by bringing the tacit knowledge to the level of consciousness; the reasoning involved will be understood by persons of similar background. Such understanding by other professionals separates tacit knowledge from the realm of intuition. Two traditional models of judgment and decision making--the Wilderness Education model and the Priest model--assume that experienced leaders recognize a problem and then think through sequential steps to arrive at an appropriate decision. These models do not recognize that many "decisions" of experienced leaders are not consciously made, but result from "preconscious" processes or habits. An experienced leader's tacit knowledge also figures in anticipation and prevention of problems, instant recognition that a problem exists, and a constant unconscious form of evaluation and decision making. Provides examples from outdoor recreation and adventure situations. (SV)