Forcing 1NT 

Responder's 1NT to an opening major is a 1-round force. Playing 2over1, the bid can have as many as 12- points, and can show a variety of hands. Opener rebids his suit with 6+, or shows a 2nd suit (4+ hearts, or 3+ minors). He jumps to the next level with these shapes and 18+ points.

Responder second bid.