Na h-Eileanan an Iar (/nə ˈhɪlənən ən jɪər/; Scottish Gaelic pronunciation: [nəˈhelanən əˈɲiəɾ]), formerly Western Isles, is a constituency of the House of Commons of the Parliament of the United Kingdom, created in 1918.

The constituency area is that of the Outer Hebrides, known also as Na h-Eileanan Siar, and has remained unchanged since its creation under the Representation of the People Act 1918 for the general election of that year.

The Scottish Boundary Commission in 1980 proposed that the seat should be extended to include the Skye and Lochalsh areas; this was overturned at a public enquiry.

Generally, considerations of geographical size, a disparate population and convenience for the MPs concerned, as well as tradition and identity, have tended to override the arguments about numerical imbalance.

Macmillan was defeated at the 1970 general election by the Scottish National Party candidate Donald Stewart – who thus became the first SNP member to be represented at Westminster.

[6] At the 2024 general election he stood as an independent gaining 10% of the vote, helping to swing the seat heavily to Labour, represented by Torcuil Crichton.