A puppy or pup is a juvenile dog, generally less than one year of age, that has not reached sexual maturity. Puppy size varies among breeds: smaller puppies may weigh , while others are . All healthy puppies grow rapidly after birth.
A puppy's coat color may change as the puppy matures, as is commonly seen in breeds such as the Yorkshire Terrier.
Reputable dog breeders raise their animals in humane conditions, provide good socialization and often formal training, and adhere to the breed standard. They are knowledgeable about major health problems associated with their breed, and with the principles of genetics, frequently undertaking specific matings to produce or refine particular desirable characteristics in their dogs. Less than scrupulous breeding operations, known as puppy mills, may provide less attention to genetics, health, prenatal care, and nutrition, and often produce puppies which are improperly socialized and in poor health.
Training of basic obedience can begin at the same time, although recommendations for how intense and how soon vary. Training for young puppies is generally recommended to be light, gentle, and fun; more like a game than an exercise. Most formal puppy classes accept puppies starting at three months of age, although some provide socialization classes for younger pups. Local dog trainers may also offer some in-home training for younger puppies.
Housebreaking can begin by the time the puppy is two to three months old, although they usually do not have enough control of their bladder to be completely housebroken until they are six months to a year old. Some find that using training pads is an effective method of housebreaking. Others prefer to use a crate training method.