New Zealand territorial flag consisting of a royal-blue field with a Union Jack (United Kingdom, flag of the) in the upper hoist quadrant and a circle of 15 white five-pointed stars in the centre of the fly portion. The flag's width-to-length ratio is 1 to 2.

The earliest flag identified with the Cook Islands was in use on the island of Rarotonga in the 1850s. It had three horizontal stripes of red, white, and red, with three blue stars in the central white stripe. A Union Jack canton was added in 1888 after Britain established a protectorate over the islands. In 1893 the stars disappeared, a badge was placed on the Union Jack, and the other islands also began displaying the flag. The Cook Islands became a protectorate under New Zealand in 1901.

On January 24, 1974, the Cook Islands acquired local autonomy and its own flag, which featured a ring of 15 yellow stars in the fly of a green field. Green stood for the islands' lush vegetation and the vitality of the people; yellow indicated their friendliness, hope, faith, and dedication; and the ring of stars represented unity for the 15 islands. The flag was subsequently altered. The new design, made official on August 4, 1979, more closely resembles the New Zealand flag (New Zealand, flag of). The Union Jack in the canton of a blue field symbolizes a peaceful ocean nation and recalls the islands' link with the Commonwealth. The white stars symbolize faith in God and the equality of the 15 islands.