In the original Catz and Dogz games (sometimes referred to as Catz 1 and Dogz 1, though the numbers were not included in the official titles of the games) the player could choose between five different breeds to adopt from in each game (Persian, Siamese, Calico, B&W Shorthair and Orange Shorthair in Catz, and Bulldog, Great Dane, Dalmatian, Daschshund, and Scottie in Dogz). Each of these breeds has its own personality, and like in later versions, the petz grow up over time. However, the player can only own one pet at a time, and all petz of the same breed look identical. There is also only a limited selection of toys.
Come Petz 2, many things changed. The amount of breeds was doubled and many new toys were introduced - furthermore, new official breeds and toys could be downloaded from Petz.com occasionally. Some breeds also became more varied in their looks. In this edition, the player can adopt an unlimited number of petz and play with any two different petz at the same time. It was made possible to put the petz 'away' through the pet door, and have the game open without any petz out. Petz may also become neglected and run away if they do not get enough attention. For the first time, when both the Catz and Dogz counterparts of the series were installed, the player could choose to merge the two together into Petz. By doing this, they could play with both catz and dogz within one game, and also have all the exclusive toys from both versions in one game.Petz 3, once again, introduced many new features. Some breeds that could only be obtained through download in Petz 2 were added to the game, bringing the total number of breeds in each version (Catz and Dogz) to 10. There were many new playscenes in and around the house, as well as some new toys (some associated with certain playscenes). It was also made possible to dress up your petz. However, the most important thing that this version introduced, is breeding. For the first time ever, two petz of the same species and opposite gender may fall in love and, after a few days of pregnancy, have their offspring. Each mating would bring forth one kitten or puppy, in which the parents' traits were combined.
Petz 4 is similar to Petz 3 in many ways. It features new playscenes (mostly of exotic places around the world), toys and clothes, but no new breeds. Litters are still one baby at a time. Voice recognition was introduced, as well as the option to easily create your own playscenes using the in-game wizard.
Petz 5 introduced new breeds, five of each species, bringing the total number of each to 15. Again, new toys and clothes were included. There are also some new playscenes, this time a mixture of 'at home' and 'around the world'. Litters now consist of up to four babies. Most toys in the game are not available right away, but have to be obtained through playing mini games in certain playscenes. New weather effects were introduced, as well as a 'Web Fun Pack', which included a number of petz' images and graphics for use on a website.