Walter Hume Long, 1st Viscount Long,, was a British Unionist politician. In a political career spanning over 40 years, he held office as President of the Board of Agriculture, President of the Local Government Board, Chief Secretary for Ireland, Secretary of State for the Colonies and First Lord of the Admiralty. He is also remembered for his links with Irish Unionism, and served as Leader of the Irish Unionist Party in the House of Commons from 1906 to 1910.

Unionism in Ireland is a political tradition that professes loyalty to the crown of the United Kingdom and to the union it represents with England, Scotland and Wales. The overwhelming sentiment of Ireland's Protestant minority, unionism mobilised in the decades following Catholic Emancipation in 1829 to oppose restoration of a separate Irish parliament. Since Partition in 1921, as Ulster unionism its goal has been to retain Northern Ireland as a devolved region within the United Kingdom and to resist the prospect of an all-Ireland republic. Within the framework of the 1998 Belfast Agreement, which concluded three decades of political violence, unionists have shared office with Irish nationalists in a reformed Northern Ireland Assembly. As of February 2024, they no longer do so as the larger faction: they serve in an executive with an Irish republican First Minister.