To many in the fi eld, the core principles of instructional design (ID) are rooted in what is known as conditions-based theory. Conditions-based theory is basically a cognitive orientation that is especially pertinent to the selection and design of instructional strategies. It is closely related to the work of Robert M. Gagné, a pioneer of ID theory and research. While Gagné saw his key principles as elements of instructional theory, his work has been applied directly to the development of the conditions-based genre of ID theory and practice. Today, there are a number of conditions-based ID theories and models which are consistent with most (if not all) of Gagné’s original principles. Recent thinking expands his original premises and often emphasizes new aspects of the learning and performance improvement processes.