This chapter joins a discussion of instructional theory that has been ongoing for nearly a century. It departs in some ways from prior discussions: (1) it considers instructional theory as a species of technological theory rather than as a type of scientific theory, a view expressed more fully elsewhere (Gibbons, 2003a), (2) it adopts the viewpoint articulated in earlier chapters of this book that there are multiple distinct bodies of technological theory that pertain to the work of instructional designers, (3) it attempts to articulate a particular view of the nature of two of those bodies of theory by describing their relationship to each other, and (4) it suggests a direction for the future exploration of additional bodies of theory, based on the writing of Vincenti (1990). Other views of possible theorydevelopment are described in Reigeluth and Carr-Chellman (Chapter 1) and Bichelmeyer, Boling and Gibbons (2006). Each of these views of the future development of theory begins from a different starting point and suggests interesting alternatives for exploration, perhaps leading to a new level of discussion of the role of theory in instructional design.