In heraldry, cadency is any systematic way to distinguish arms displayed by descendants of the holder of a coat of arms when those family members have not been granted arms in their own right. Cadency is necessary in heraldic systems in which a given design may be owned by only one person at any time, generally the head of the senior line of a particular family.

As an armiger's arms may be used 'by courtesy', either by children or spouses, while they are still living, some form of differencing may be required so as not to confuse them with the original undifferenced or "plain coat" arms. Historically, arms were only heritable by males, and therefore cadency marks had no relevance to daughters; in the modern era, Canadian and Irish heraldry include daughters in cadency.

These differences are formed by adding to the arms small and inconspicuous marks called brisures, similar to charges but smaller. They are placed on the fess-point, or in-chief in the case of the label. Brisures are generally exempt from the rule of tincture. One of the best examples of usage from the medieval period is shown on the seven Beauchamp cadets in the stained-glass windows of St Mary's Church, Warwick.