Na h-Eileanan an Iar (/nə ˈhɪlənən ənˈjɪər/; Scottish Gaelic pronunciation: [nəˈhelanən əˈɲiəɾ]), formerly the Western Isles, is a constituency of the Scottish Parliament (Holyrood) covering the council area of Na h-Eileanan Siar.

The Na h-Eileanan an Iar constituency is part of the Highlands and Islands electoral region; the other seven constituencies are Argyll and Bute, Caithness, Sutherland and Ross, Inverness and Nairn, Moray, Orkney, Shetland and Skye, Lochaber and Badenoch.

From the 2005 United Kingdom general election, however, the name of the Westminster (House of Commons) constituency was changed to Na h-Eileanan an Iar.

The Holyrood constituency covers Na h-Eileanan Siar (the Western Isles council area), comprising its nine wards: Barraigh, Bhatarsaigh, Eirisgeigh agus Uibhist a Deas; Beinn Na Foghla agus Uibhist a Tuath; Na Hearadh agus Ceann a Deas Nan Loch; Sgir’ Uige agus Ceann a Tuath Nan Loch; Sgire an Rubha; Steòrnabhagh a Deas; Steòrnabhagh a Tuath; Loch a Tuath; An Taobh Siar agus Nis.

In recent years, however, it has become increasingly safe for the Scottish National Party.