The Flag of Hawaii (Hawaiian: Ka Hae Hawaiʻi), also known as the Hawaiian flag, is the official flag of the U.S. state of Hawaii. It consists of a field of eight horizontal stripes, in the sequence of white, red, blue, white, red, blue, white, red, with a British Union Jack depicted as a canton in the upper-left corner. The flag has been in use since 1845.

Captain George Vancouver of the British Royal Navy visited the Hawaiian Islands on three occasions during his 1791 to 1795 expedition. At this time, the Hawaiian Islands were divided among several warring chiefdoms. In February 1794, while at anchorage in Kealakekua Bay off the Hawaiʻi island, Vancouver reached a diplomatic agreement with the king (or aliʻi) of that island, Kamehameha, who would later unite all the Hawaiian islands and become the first ruler of the Kingdom of Hawaiʻi. Vancouver believed that the agreement reached meant Hawaiʻi island was being ceded to Great Britain, but historians have argued that the Hawaiians saw the agreement as establishing a protectorate. After the proceedings on Vancouver's vessel, a British flag was presented, taken ashore and raised. The flag was either a British Union Jack, or a Red Ensign as used by the Royal Navy, which features a Union Jack in the canton. In 1801, the British Union Jack added a Saint Patrick's Cross when Ireland joined with Great Britain in a political union. Both pre- and post-1801 versions of the Red Ensign served as the unofficial flag of the Kingdom of Hawaiʻi until 1816.

There is an unverified anecdote that, during the War of 1812 (fought between the United Kingdom and the United States from 1812 to 1815), Kamehameha became aware of the nationalist meaning of flags. To avoid offending either side, he designed a new flag for his kingdom which combined elements of both the British Union Jack and the flag of the United States.

In April 1816, Kamehameha purchased a brig from Scottish Captain Alexander Adams, and arranged for Adams to take command of the ship, which was renamed Kaʻahumanu after the wife of Kamehameha. As part of the transfer ceremony, Adams wrote that he was "honored to take command under the Flag of His Majesty" though he does not describe the flag. The next year, in March 1817, the Kaʻahumanu became the first Hawaiian vessel to sail to a foreign port (Canton, China) under a "distinct" Hawaiian flag. In one source, this is described as: "A St. George and St. Andrews Cross in the corner filled in with blue, with field consisting of red and white stripes" which virtually matches the ensign of the East India Company though another source describes "red, white and blue stripes added to a Union Jack".

The Russian navigator Vasily Golovnin, based on a visit to Oʻahu in 1818, describes seeing a "national flag" which "consists of seven stripes: red, white, blue, red, white, blue and red, with the English Union Jack in the corner".

Until 1845, visitors to the Hawaiian Islands reported various versions of the flag with different numbers of stripes and colors.

In 1843, either as an inadvertent mistake, or as a symbolic "reversal" gesture in the wake of the Paulet affair - a five-month-long, unofficial occupation of Hawaii by a British naval officer - the flag design was specified to have eight stripes: a white stripe on top followed by the sequence red, blue, white, red, blue, white, red. This new flag was officially unfurled on May 25, 1845, at the opening of the legislative council and remains the same design as used today.

The canton of the flag of Hawaii contains the Union Flag of the United Kingdom, prominent over the top quarter closest to the flag mast. The field of the flag is composed of eight horizontal stripes, symbolizing the eight major islands (Hawaiʻi, Maui, Kahoʻolawe, Lānaʻi, Molokaʻi, Oʻahu, Kauaʻi, and Niʻihau). The color of the stripes, from the top down, follows the sequence: white, red, blue, white, red, blue, white, red. The colors "red", "blue", and "white" are not explicitly defined.