In many naming systems, the names of cats and dogs differ clearly from each other, both morphologically-phonologically and semantically. This paper analyses Finnish cat and dog names from this viewpoint. The data for this analysis come from the official name day calendars for cats and dogs in Finland, which were published by the Almanac Office at University of Helsinki in 2012. In the Finnish language, cat names are often onomatopoetic and refer to a cat’s meowing, purring, hissing or growling. They typically begin with an /m/ and contain the phonemes /i/, /r/ and /s/. Dog names, in their turn, are formed with different derivational suffixes such as -ki, -kke, -kku, -ppe, or -ssu. They are formed to be short and easy to pronounce so that they function in calling the dog. Semantically, many cat and dog names describe the animal and refer to the characteristic features of the individual or the species. Hence, cat names reflect the catness of the animal, and dog names the dogness of the animal. Besides these differences, one can find many similarities in the naming of cats and dogs in Finland. One of the current trends is the increased use of personal names for pets, which can be seen as a sign of increasing humanisation of animals in modern society. Today, several pet names are also adopted from popular culture, and from many different languages.