Family crests developed from coats of arms. Early coats of arms were cloth tunics that knights wore over their armor. Because a knight's armor was a symbol of his achievements, the coat of arms became a status symbol, and the family crest developed to show a knight's lineage.
Early heraldic crests were printed on metal fans and set atop a knight's helmet. Because these designs were rather impractical and added unnecessary weight, knights rarely wore crests into battle. Instead, they saved the crests for tournaments and special ceremonies.
According to medieval British heraldry rules, only the firstborn son of a couple inherited the right to wear his father's crest. If the family had only daughters, the crest was instead inherited by the firstborn grandson. In many heraldry traditions, the husband and wife combined their respective family crests to form a hybrid version. Women could wear crests in certain cultures, but their crests had different designs than those of men.
Modern countries have different rules for crest inheritance. Ireland, for example, allows individuals to petition for the right to bear a coat of arms or use their family crest. France requires that the crest is legally registered with a notary or clerk of court.