Monadenia fidelis, commonly known as the Pacific sideband, is a medium-sized species of air-breathing land snail.

[2] At 22 to 36 mm wide, it is the largest land snail species in the state of Washington.

[3] M. fidelis is endemic to the Pacific Coast of North America, and is found in California, Oregon, Washington, British Columbia, and Alaska.

There is a significant amount of morphological variation among individuals of this species, and several distinct subspecies are recognized.

While populations of this snail display distinct morphotypes, recent research in genomics indicates that there is gene flow between recognized subspecies, and even between M. fidelis and other species in the genus Monadenia.