Dogs as an assistive aid for people with disabilities date as far back in time as the first century CE. Today, dogs are used in various settings to help and assist humans. 'Assistance dogs' is an umbrella term for guide dogs, hearing dogs and service dogs. They are custom trained to help and support their owners in their everyday life and thereby give them greater independence. Dogs who perform dog-assisted interventions are another type of working dog, where the dog and the owner work together as a team visiting people with various needs in different settings such as hospitals and nursing homes. These visits aim to strengthen people's inner motivation, using the dog as an external motivator. There is a lack of evaluations of working dogs in the health technology assessment context, and in the health economic evaluation context. Hence, there is a need for structured analyses that include both the short-and long-term effects and the costs of assistance dogs and dog-assisted interventions.The overall aim of this thesis is to explore and assess the use of assistance dogs and dog-assisted interventions.The research questions were investigated using a variety of methods. In paper I, inferential statistical analysis was used to analyse patient-reported outcomes measures. In paper II, a thematic content analysis was employed to explore the experiences of service and hearing dogs. To study the long-term cost-effectiveness of physical service dogs and diabetes alert dogs, a decision analytic model was used in paper III. The input data in studies I, II, and III was obtained from the Service and Hearing Dog Project. In paper III, the data was also supplemented with information from published literature and expert opinions. Paper IV investigated the effects and cost-effectiveness of dog-assisted interventions, and takes the form of a systematic review.Paper I showed that a service or hearing dog have positive impact on its owner's health-related quality of life, well-being and activity level. Paper II showed that owners of service or hearing dogs experienced both positive physical and psychosocial effects from their dog. Negative experiences were also identified, for example being denied access to public places and negative attitudes from other people. Paper III showed that physical service dogs and diabetes alert dogs are cost-effective in comparison with regular companion dogs, resulting in both lower costs and a gain in QALYs. The one-way sensitivity analysis did not change the results, but the probabilistic sensitivity analysis showed that the results were uncertain. Synthesizing Lars-Åke Levin, my supervisor, for generously sharing your great knowledge and experiences. For all the time you put into reading my work and guiding me forward. Your encouragement and praise have made me grow, both professionally and personally. Jenny Alwin, my co-supervisor, for being genuinely supportive and for teaching me the importance of being accurate and transparent. Your door has always been open, and you have always shown great confid...