The overarching goal of this thesis was to improve the understanding of canine resource guarding (RG), which is defined as the use of avoidance, threatening, or aggressive behaviours to retain control of items in the presence of a person or other animal. Results from the first study, an online discussion board involving fourteen companion animal behaviour experts, identified most participants prefer to describe the behaviour as "resource guarding" due to the positive perception and interpretation of the term by dog owners, and the potential for inclusion of non-aggressive behaviour patterns such as avoidance and rapid ingestion. The second study examined dog owners’ (n = 1438) ability to identify three different forms of resource guarding (i.e., avoidance, rapid ingestion or aggression). The non-aggressive patterns of RG, and those involving threatening aggression (e.g., growling, teeth baring) were significantly more difficult for participants to identify compared to biting aggression. Findings were used to develop a RG identification tool to ensure owners were able to correctly classify different types of RG in subsequent studies. For the third and fourth studies, dog owners were recruited (n = 3068) to complete a survey to determine factors associated with the expression of RG in the presence of either people or other dogs, respectively. Neutered males, mixed breeds, and dogs with higher levels of impulsivity and fearfulness were significantly more likely to display people- and dog-directed RG aggression compared to dogs of other sexes, breeds, and lower levels of impulsivity and fearfulness. Training dogs to "drop" and "leave" items was associated with decreased risk of both people- and dog-directed RG aggression while removing the food bowl during mealtimes was associated with increased risk of people-directed RG aggression. In addition, RG aggression had a negative association with RG avoidance and rapid ingestion in the presence of dogs; however, no such relationship was found in the presence of people, suggesting that RG behaviour patterns are more flexible when humans are involved. This thesis has advanced the current understanding of RG in dogs, as well as informed areas for future longitudinal studies to further understand the etiology of RG behaviour patterns.