The formative period for a dog occurs in its first year of life. The first few months account for a large part of this development. When puppies are born they are very reliant on their mother. Born with their eyes and ears sealed shut, they huddle near each other and their mother for warmth and food. During the first three weeks, puppies sleep 90 percent of the time and eat 10 percent. Healthy puppies are born pink and firm and gain weight rapidly. During the first month a puppy's senses start to develop. Their eyes will open, teeth will start to come through and they will begin standing, walking, barking and wagging their tail.

Puppies begin socialization shortly before their second month. In the beginning they are primarily influenced by their littermates. Through playing and interacting, puppies learn about themselves and their surroundings. This type of learning continues for several months. Puppies are ready to be adopted around 8 to 10 weeks of age. At this point people are influencing them as much if not more than the other puppies. This is a good time to start the basics of training such as housetraining, as they are starting to gain physical coordination. They will also experience fear for the first time.

Between three and six months puppies will begin to develop pack behavior. They will start to see their place within their social system. They will also start to develop their adult teeth and begin teething. Between six and eighteen months puppies will be influenced primarily by pack/family members, and will chew as a way of exploring their territory. They will physically mature during this period, becoming an adult.