Katmai was originally designated a National Monument in 1918 to preserve the features associated with one of the most powerful volcanic eruptions ever recorded. Later expansions and the change in status to Park and Preserve were not focused around geologic activity but rather on the importance of protecting Katmai's remarkable wildlife. One of the primary purposes of Katmai National Park and Preserve, based on legislation, is to: protect habitats for and populations of fish and wildlife, including, but not limited to, high concentrations of brown bears and their denning areas, and maintain unimpaired the watersheds and water habitat vital to red salmon spawning.

Besides brown bear, Katmai provides a protected home to moose, caribou, red fox, wolf, lynx, wolverine, river otter, mink, marten, weasel, porcupine, snowshoe hare, red squirrel, and beaver. Marine mammals include; sea lions, sea otters, and hair seals. Beluga, killer, and gray whales can also be seen along the coast of the park.