Louisbourg is a former town in southeastern Cape Breton Island, in Nova Scotia, Canada. The name was given by French military forces who founded a large fortified seaport on the southwest part of the harbour (see Fortress Louisbourg), in honour of Louis XV.

Pronounced "Lewisburg" by its largely English population, the present community has been identified by slightly different spellings over the years by both locals and visitors: Louisbourg and Louisburg. The latter name was formalized by the Sydney & Louisburg Railway which used Louisbourg Harbour's ice-free waters as a winter coal port. The spelling Louisbourg is formally recognized as the correct version by the Geographic Names Board of Canada and Nova Scotia's coordinator for geographic names.

Incorporated in 1901, Louisbourg was one of several municipal units which were amalgamated under the Cape Breton Regional Municipality in 1995.