While most any family pet could be considered a companion, the best companion dogs have certain qualities. First, they must be suited for living indoors. They should be calm and not aggressive around other people or animals. A dog should be compatible with a person's lifestyle and personality. Large dogs may not be suitable for very young children. Older people are increasingly choosing smaller dogs. Therapy dogs and emotional support dogs provide comfort to people with certain conditions. Often they belong to staff members of hospitals or institutions. Some dogs are certified as companion dogs and are selected for certain qualities.