Copenhagen is a system of specialized jump overcalls that show two-suited hands. After 1-of-a-suit, the conventional overcalls are:
|2NT||At least 5-5 in the lowest two unbid suits|
|3||At least 5-5 in the top and bottom unbid suits|
|3||At least 5-5 in the highest two unbid suits|
All of partner's responses are natural.