This article introduces and develops a comprehensive scale named Octomodal Mental Imagery (OMI) to measure various aspects of imagination and prospection. OMI is developed and validated by conducting three rigorous studies and six data collections. In the first study, using the phenomenology approach, a detailed internal experience of the imagination process was carefully recorded. In the second study, the potential manifest variables to measure imagination/prospection were developed and a general configuration of the questionnaire was determined. In the third study, through three data collections, two versions of long (original) and short OMI were thoroughly screened, refined, and validated. Furthermore, from the measurement and structural perspectives, the conceptualization of imagination was compared to prospection. Our results substantiate OMI as a reliable and valid scale to be used in and out of hedonic consumption contexts.