When partner opens 1NT and you hold a 4-card major (♥ or ♠) with 11+ HCP, bid 2♣ (Stayman) to ask if partner has a 4-card major.

Partner responds: 2♦ = no 4-card major  ·  2♥ = 4+ hearts  ·  2♠ = 4+ spades (denies 4 hearts).

After partner's response — if a major fit is found, raise to 3M (invite, 11–12 HCP) or 4M (game, 13+ HCP). With no fit, bid 2NT (invite) or 3NT (game).