PSNI is the short official name for the Police Service of Northern Ireland — the police force that works in Northern Ireland, which is part of the United Kingdom. You see the letters in news, on reports, and on uniforms. It is not the police of the Republic of Ireland, the country south of the border; that is a different force in a different country. The PSNI took over from an older force in 2001, after the peace talks. In everyday talk there, people still often just say “the police”; PSNI is the formal label.