A gale warning is an advisory or warning issued by the local competent authority in maritime countries about the existence of winds of gale-force or above or the imminent occurence of gales at sea. The purpose of gale warnings is to allow shipping to take precautionary actions to ensure their safety at sea.

In the United States by the National Weather Service to areas experiencing, or about to experience, winds within the range of 39 to 54 miles per hour (or approximately 37 to 51 knots).

In the UK gales warnings are issued by the Meteorological Office and are broadcast by radio four times a day at fixed times on 198 metres in the shipping forecast, part of the broadcast output of BBC Radio 4. Warnings are issued for sea areas surrounding the UK for all predictions of winds of Beaufort Force 8 or above, the forecasts extending as far north as Iceland and as far south as southern Spain.

Though usually associated with tropical cyclones, winds strong enough to catalyze a gale warning can occur in other conditions as well, including from anticyclones, or high-pressure systems, in the continental interior. However the warning is most commonly issued in coastal areas, and is primarily directed at marine rather than land-based interests — and the term high wind warning is often substituted for "gale warning" in non-maritime settings.

The insignia for a gale warning is two red triangular flags, one placed above the other (only one such flag denoting a small craft advisory).