Canine behavior problems are a significant public health concern in the USA, as well as being a major threat to the welfare and survival of pet dogs. Despite the extent of the problems posed by canine behavior problems, relatively little is known about their overall prevalence in the pet dog population, or the reasons why they develop in some dogs but not in others. Efforts to understand the distribution and development of behavior problems are currently hampered by the fact that (a) canine behavior is difficult to observe and record in the home environment using conventional methods, and (b) there is no widely accepted “gold standard” system for describing and classifying these problems. The proposed study is seeking to overcome these difficulties by completing the development and validation of a new behavioral measurement instrument, the University of Pennsylvania Behavioral Assessment and Research Questionnaire (PennBARQ). This instrument shows considerable promise both as a research tool for studying canine behavioral problems at the population level, and as a reliable method for screening individual dogs for the presence of behavior problems.