Dogs and cats fall into one of two categories: purebreds or mixed breeds. The only significant difference between the two is that purebreds, because their parents and other ancestors are all members of the same breed, generally conform to a specific "breed standard." This means that you have a good chance of knowing what general physical and behavioral characteristics a puppy or kitten of that breed is likely to have.
The size, appearance, and temperament of most mixed breed dogs can be predicted as well. After all, mixed breeds are simply combinations of different breeds. So if you can recognize the ancestry of a particular mixed breed dog or cat, you can see how a puppy or kitten is likely to look as an adult.
Some people think that when they purchase a purebred, they're purchasing a guarantee of health and temperament, too. This is simply not true. In fact, the only thing the "papers" from purebred dog and cat registry organizations certify is that the recording registry maintains information regarding the reported lineage and identity of the animal.
Mixed breeds, on the other hand, offer several advantages that prospective pet owners may fail to consider. For example, when you adopt a mixed breed, you get the benefit of two or more different breeds in one animal. You also get a pet who is less prone to genetic defects common to certain purebred dogs and cats.
Whether you're thinking about adopting a dog or cat, purebred or mixed breed, it's important to make sure your favorite type of animal fits with your lifestyle. You may love border collies, for example, but these active dogs likely aren't a good match for busy apartment dwellers living in a city. So first become knowledgeable about what kind of animal you want and about what it takes to be a responsible pet caregiver.
There are several types of organizations from which you can adopt a companion animal, whether purebred or mixed breed. Not all sources are the same, however, so it's important to learn as much as you can, and then choose carefully.