A Black Bag Job or Black Bag Operation is a covert entry action undertaken by a police force or intelligence agency. A black bag job should not become known to its target, so violence or confrontation are to be avoided.

Reasons for a black bag job include planting surveillence equipment and finding and copying documents, computer data or cryptographic keys.

The term comes from the black bags formerly used by intelligence services to carry the equipment required for such operations.

Reference

Sir Peter Wright. Spy Catcher: The Candid Autobiography of a Senior Intelligence Officer. Penguin USA, 1987. ISBN 0670820555.