Cypress Hills Interprovincial Park, Interprovincial park and dark-sky preserve in Alberta and Saskatchewan, Canada

Cypress Hills Interprovincial Park covers two blocks: the 345 km² West Block, straddling the Alberta–Saskatchewan boundary, and the 58 km² Centre Block in Saskatchewan. The plateau rises up to 200 m above the prairie, reaching 1,468 m at Head of the Mountain in Alberta and 1,392 m across the border, Saskatchewan's highest point. Battle Creek runs through the centre.

Cypress Hills Provincial Park was established in Saskatchewan in 1931 and in Alberta in 1951. On 25 August 1989 the two provinces signed an agreement on ecosystem management, education and park promotion, creating Canada's first interprovincial park. Fort Walsh National Historic Site, on the Saskatchewan side of the West Block, joined the partnership in 2000.

The name is misleading: no cypress grows here. The hills were named for the jack pine, which early surveyors took for a cypress species. The park's astronomical culture is documented: on 18 August 2001 Vance Petriew discovered comet 185P/Petriew during the Saskatchewan Summer Star Party, and in 2004 the park was declared a dark-sky preserve.

The West Block lies between Alberta Highway 41, Elkwater, Saskatchewan Highway 615, Saskatchewan Highway 271 and Fort Walsh; the Centre Block is in Saskatchewan west of Highway 21. The Alberta side holds Elkwater Lake, Spruce Coulee Reservoir and Reesor Lake, with over 50 km of hiking and mountain biking trails. In winter, summer campgrounds become 9 km of cross-country ski trails and 3.8 km of snowshoe trails.

On 18 August 2001, during the Saskatchewan Summer Star Party, Vance Petriew discovered a comet from the park; it was later named 185P/Petriew. In 2004 Saskatchewan Parks, Alberta Community Development, Parks Canada and the Royal Astronomical Society of Canada declared the park a dark-sky preserve, and in 2011 the Cypress Hills Observatory and a yurt classroom opened.