Many groups, such as rescue and service-dog programs, are interested in assessing dogs’ personalities. These groups often need to assess large numbers of dogs with limited resources (e.g., in terms of facilities, trained assessors, time, money). To meet these groups’ requirements, an assessment tool that measures canine personality rapidly and is demonstrably reliable and valid is needed. The Dog Personality Questionnaire (DPQ) was developed to fill this gap. This dissertation describes a series of six studies designed to develop and evaluate the DPQ. To ensure that the final instrument built on previous research and was based on a comprehensive item pool, 1,200 descriptions were culled from the dog-personality assessment literature, shelter assessments, and dog experts’ input (e.g., researchers, trainers, veterinarians). Three expert judges narrowed this list to 360 items. In Study 1, these items were administered to 152 participants who gave feedback on the items’ applicability and ease of use. In Study 2, exploratory factor analysis was used to determine the number of factors underlying the 360-item questionnaire, based on 3,737 participants’ ratings of their dogs. Convergent criteria favored five factors, labeled as Fearfulness, Aggression towards People, Aggression towards Animals, Activity/Excitability, and Responsiveness to Training. Narrower facets within each factor were also identified. On the basis of item analyses, the questionnaire was shortened to 102 items. In Study 3, the 102-item questionnaire was administered to 2,556 new participants and further exploratory and confirmatory factor analyses were used to examine the robustness of the five-factor solution. Items were then evaluated in terms of factor- and facet-loadings, content validity, internal consistency, and other criteria in order to shorten the questionnaire to a more manageable, 75-item form, and an even briefer 45-item form. In Studies 4-6, the psychometric properties of the 75-item and 45-item DPQ were further evaluated. The DPQ was shown to have acceptable levels of inter-rater reliability (Study 4), test-retest reliability (Study 5), and predictive validity (Study 6). Discussion focuses on evaluating how well the DPQ meets the criteria that guided its development. / text