U.S. state flag consisting of a quartered design of alternating red-white and black-yellow panels.

Alone of the 13 original states, Maryland has a state flag based on a flag flown under British rule. According to the laws of heraldry, the personal banner of the Lords Baltimore, who were the proprietary owners of Maryland, was by extension that of the territory they ruled. In 1638 Leonard Calvert (Calvert, Leonard), son of Sir George Calvert, the first Lord Baltimore, wrote to his brother Cecilius that he had flown the Calvert banner in battle, and through the 17th and 18th centuries the flag continued in use. The Calvert coat of arms (arms, coat of) consisted of six vertical stripes, alternately yellow and black, with a diagonal stripe (from the upper hoist to lower fly) of counterchanged colours—that is, black where the diagonal crossed a yellow stripe and vice versa. As is the case with most early heraldic arms, there is no known symbolism in the yellow-and-black design; it was simply distinctive. In contrast, the Crossland family (maternal family of Sir George Calvert) had a coat of arms with clearer symbolic origins. It made a pun on the family name by showing a quartered white-and-red shield bearing a counterchanged cross botonée (a cross whose arms end in three balls).

Although traditional heraldry fell into disuse in the 13 British colonies during the American Revolution (1775–83), the arms of the Lords Baltimore were never forgotten. Various designs, including badges worn by Maryland troops during the Civil War (American Civil War) (1861–65), incorporated these symbols. On March 9, 1904, an armorial banner combining the arms of the Calverts and Crosslands was officially adopted as the state flag. A cross botonée frequently serves as the finial for the pole on which the flag is displayed.