The Ulster Defence Association (UDA) is an Ulster loyalist paramilitary group in Northern Ireland. It was formed in September 1971 as an umbrella group for various loyalist groups and undertook an armed campaign of almost 24 years as one of the participants of the Troubles. Its declared goal was to defend Ulster Protestant loyalist areas and to combat Irish republicanism, particularly the Provisional Irish Republican Army (IRA). In the 1970s, uniformed UDA members openly patrolled these areas armed with batons and held large marches and rallies. Within the UDA was a group tasked with launching paramilitary attacks that used the cover name Ulster Freedom Fighters (UFF) so that the UDA would not be outlawed. The British government proscribed the UFF as a terrorist group in November 1973, but the UDA itself was not proscribed until August 1992.

Ulster loyalism is a strand of Ulster unionism associated with working class Ulster Protestants in Northern Ireland. Like other unionists, loyalists support the continued existence of Northern Ireland within the United Kingdom, and oppose a united Ireland independent of the UK. Unlike other strands of unionism, loyalism has been described as an ethnic nationalism of Ulster Protestants and "a variation of British nationalism". Loyalists are often said to have a conditional loyalty to the British state so long as it defends their interests. They see themselves as loyal primarily to the Protestant British monarchy rather than to British governments and institutions, while Garret FitzGerald argued they are loyal to 'Ulster' over 'the Union'. A small minority of loyalists have called for an independent Ulster Protestant state, believing they cannot rely on British governments to support them. The term 'loyalism' is usually associated with paramilitarism.