The Outer Hebrides (Scottish Gaelic: Na h-Eileanan Siar, IPA: [nə ˈhelanən ˈʃiəɾ]) also known as the Western Isles and the Long Island, is an island chain off the west coast of Scotland. The islands are geographically contiguous with Comhairle nan Eilean Siar, one of the 32 unitary council areas of Scotland. They form part of the Hebrides, separated from the Scottish mainland and from the Inner Hebrides by the waters of the Minch, the Little Minch and the Sea of the Hebrides. Scottish Gaelic is the predominant spoken language, although in a few areas English speakers form a majority.

Most of the islands have a bedrock formed from ancient metamorphic rocks and the climate is mild and oceanic. The 15 inhabited islands have a total population of about 26,500 and there are more than 50 substantial uninhabited islands.

There are various important prehistoric structures, many of which pre-date the first written references to the islands by Roman and Greek authors. The Western Isles became part of the Norse kingdom of the Suðreyjar, which lasted for over 400 years until sovereignty was transferred to Scotland by the Treaty of Perth in 1266. Control of the islands was then held by clan chiefs, principal of whom were the MacLeods, MacDonalds, Mackenzies and MacNeils. The Highland Clearances of the 19th century had a devastating effect on many communities and it is only in recent years that population levels have ceased to decline. Much of the land is now under local control and commercial activity is based on tourism, crofting, fishing, and weaving.