The Presbyterian Church in Ireland is the largest Presbyterian denomination in the Republic of Ireland, and the largest Protestant denomination in Northern Ireland. Like most Christian churches in Ireland, it is organised on an all-island basis, in both Northern Ireland and the Republic of Ireland. The church has approximately 210,000 members.

Presbyterianism is a Reformed (Calvinist) Protestant tradition named for its form of church government by representative assemblies of elders. Though there are other Reformed churches that are structurally similar, the word Presbyterian is applied to churches that trace their roots to the Church of Scotland or to English Dissenter groups that formed during the English Civil War.