The RUC was the police force in Northern Ireland for most of the twentieth century. The letters stand for Royal Ulster Constabulary. Constabulary is just an old, formal word for a police force; Ulster is a name for that part of Ireland; Royal tells you it answered to the British crown. In 2001 it was stood down and replaced by a new force, the PSNI — the Police Service of Northern Ireland. People still say RUC when they talk about the years of the Troubles, the long and bitter conflict there. Though actually this is not a warm, simple name for everyone. Many Catholic and nationalist families felt the RUC was on the Protestant, unionist side, and the change of name was part of trying to build a police service the whole community could trust. You will meet it in history books, news about the past, and crime stories set in Northern Ireland. It is always written in capital letters. It is not a general word for police, and it is not the name of the force that works there now.