Emotions are an integral part of animal welfare. Facial expressions are increasingly used as a noninvasive method for assessing the emotional state of animals. Dogs (Canis familiaris) are closely related to humans,and facial expressions are crucial for interspecies communication and emotional expression. This paper reviews the neurobiological mechanisms of facial expressions and the anatomical structure of the facial muscles and their evolution in dogs, the analogy between dog and human facial expressions, and the expression of various parts of the dog’s face under different emotions. These studies demonstrate that dog’s facial expressions can be used as a potential indicator of animal welfare, and that dogs can be used as a model animal for studying interspecies facial emotional communication. The use of dog’s facial expressions to assess emotions will aid multidisciplinary research, including in the fields of neuroscience, psychopharmacology, animal behavior, and animal welfare.