The flag of Martinique, an overseas region of France, does not have an official flag that exclusively represents the island. However, there is a popular and widely recognized unofficial flag known as the "Snake Flag" or "Serpent Flag".

The Snake Flag has a blue field (#0055A4) with a white cross dividing the flag into four equal quadrants. The cross width is 1/5th of the flag's height. In the upper-right quadrant (canton), there is a white snake, specifically a fer-de-lance, coiled up and facing left.

The aspect ratio of the flag is 2:3, meaning it measures 2 units wide by 3 units high. While specific dimensions can vary depending on production, the proportions remain constant.