Loneliness is extremely common, highly unpleasant, and the health consequences have been reported to rival those of smoking and obesity (House et al., 1988). It is widely believed that pets can help to alleviate loneliness. This belief is consistent with research that suggests pets can provide companionship similar to that provided by humans. Having first reviewed the literature on loneliness and the role of pets in providing companionship and alleviation of loneliness, a theory was articulated that pets should help to alleviate loneliness. The remainder of this thesis sought to test this theory. Three hypotheses were derived from the theory that pets can help alleviate loneliness: pet owners will be less lonely than non-pet owners; pet separation will be associated or will lead to increased loneliness; and, pet acquisition will lead to decreased levels of loneliness. Seven empirical studies were conducted, of which six directly tested one or more of the three hypotheses. Each hypothesis was tested at least twice. Amongst samples recruited from the general population, no quantitative evidence was found to reject any of the three null hypotheses: pet owners were no less lonely than non-pet owners; pet separation was neither associated with higher loneliness nor led to increased levels of loneliness; and pet acquisition did not lead to reduced levels of loneliness. There was some qualitative evidence that if people acquired a pet to help with loneliness they believed it was helpful. These findings did not appear to be affected by whether or not the person-pet relationship was described as 'close' or the species of pet. Amongst a sample of deaf people who were at high risk of loneliness, no evidence was found that pet owners or hearing dog owners were less lonely than non-owners. Nor was there significant evidence that hearing dog acquisition led to lower levels of loneliness. It was concluded that insofar as none of the three hypotheses were supported by the data, the theory that pets help to alleviate loneliness was not supported amongst the general population. It was proposed that the belief that pets alleviate loneliness might endure simply because it is a pleasing and agreeable belief. Alternatively, people may see what they want to see. However, it is also possible that the quantitative methods used in psychology simply fail to reflect the qualitative benefits of pet ownership, or that there are people for whom pets alleviate loneliness, but they are specific subgroups of the population.