Wilderness therapy program theory is reasoned to be, as Weiss (1997) describes, a tacit theory, or one which is implied and not clearly articulated. This is evidenced by several meta-analyses which have consistently found either very limited or no detailed descriptions of the wilderness therapy programs under investigation. The purpose of this paper is to address this lack of articulated and empirically grounded theory by empirically examining the practice of four established wilderness therapy programs, all licensed by their respective state agencies and accredited by national accreditation organizations. A multi-site case study approach was used to elicit program theory that included interviews and focus groups with key staff at each program, participant observation of the process in the field, and interviews and observation of client case studies. An emergent theory is presented that consists of elements of program impact theory (who the programs serve and anticipated outcomes) as well as program process theory (how the programs are organized and how they deliver services). Implications and potential uses of the emergent theoretical framework are discussed. (Contains 3 figures and 1 note.)