The Theory of Planned Behavior (TPB) has been extensively used in predictive studies, but there have been considerably fewer experimental tests of the theory. One reason for this is that the guidance on developing concrete intervention strategies from the abstract theory is vague, and there are few exemplars of how to do this. The aim of this article is to provide such an exemplar. The development of an intervention to increase walking in the general public is described, based on the TPB, extended to include postvolitional processes. Identification of target constructs, elicitation of key salient beliefs underpinning these constructs, selection of appropriate behavior change techniques, and technique refinement. Each step is based on available evidence and consistent with theory. Perceived behavioral control (PBC) was identified as the key determinant of walking intentions, with an "intention-behavior gap" noted. A brief intervention was developed, using techniques to increase PBC by rehearsal of previous successful performance of behavior, along with planning techniques to translate motivation into behavior. This systematic approach taken should provide a model for others. The intervention has demonstrated efficacy in producing large changes in objectively measured walking behavior, in 2 separate evaluations reported elsewhere.