Muir Beach, Coastal nude beach in Marin County, United States.

Muir Beach is a coastal area along the Pacific Ocean where sand and large rock formations shape the shoreline in different ways. The beach transitions gradually into the water and features a natural landscape typical of Northern California's rocky shores.

The beach was originally called Bello Beach but was renamed to benefit from the fame of nearby Muir Woods National Monument. In the 1960s the location became a center for experimental culture and countercultural gatherings.

Muir Beach takes its name from the naturalist John Muir, though the strand was earlier called Bello Beach; the renaming tied it to nearby Muir Woods National Monument. In the 1960s the cove drew countercultural gatherings, and clothing-optional use has long been part of its reputation. Visitors today share the sand with harbour seals hauled out at the mouth of Redwood Creek.

Access to the beach comes through a short footpath from the parking area that is straightforward to locate. Fire rings are available seasonally and their availability changes depending on the time of year.

Behind the beach sits a lagoon that provides habitat for rare fish species and endangered amphibians rarely noticed by visitors. This ecological value makes the location important far beyond what most people see on the sand.