There is no universally accepted definition of quality of life (QoL) or welfare in animals. While the terms are sometimes used interchangeably, they are often treated as distinct concepts. The “Five Freedoms” have long served as a basis for assessing animal welfare, especially in livestock, while QoL is a term more commonly used in companion animal care, focusing on the animal’s subjective experience. Research has shown that veterinarians tend to better assess medical or pain-related aspects of welfare, whereas animal caretakers often have better insight into the animal’s psychological state, suggesting the benefit of combining the two perspectives. Validated questionnaires are essential for thorough evaluations, as they account for the many dimensions of QoL or welfare. Generally, questionnaires can be classified into two main types: disease-specific tools and generic instruments. Disease-specific questionnaires can detect small changes in animals with a certain disease, while generic instruments are less sensitive but can be used in animals, regardless of their health status. In human medicine, generic instruments have been developed that convert QoL into a single numerical value, also called “utility.” One of these instruments has been preliminarily created for use in dogs, i.e., the “dog health utility index.”