The Regional District of Okanagan-Similkameen (RDOS) is in southern British Columbia, adjacent to the U.S. state of Washington.

It is bounded by Fraser Valley Regional District to the west, Thompson-Nicola Regional District and Regional District of Central Okanagan to the north, Regional District of Kootenay Boundary to the east, and by Okanogan County, Washington to the south.

The district covers a land area of 10,413.44 square kilometres (4,020.65 sq mi).

The municipalities of RDOS are Penticton, Summerland, Osoyoos, Oliver, Princeton, and Keremeos.

[5] According to the 2011 Census, 84.43% of Okanagan-Similkameen's population have English as mother tongue; German is the mother tongue of 2.99% of the population, followed by Punjabi (2.86%), French (1.90%), Portuguese (1.06%), Dutch (0.80%), Ukrainian (0.42%), Hungarian (0.41%), Spanish (0.41%), and Italian (0.39%).