Isabella of Mar (fl. 1290s) was the first wife of Robert Bruce VII, Earl of Carrick. Isabella died before her husband was crowned (as Robert I) King of Scotland. She and her husband were the grandparents of Robert II, King of Scotland.
Isabella was the daughter of Domhnall I, Earl of Mar (died ×1297) and Elena, daughter of Llywelyn ap Gruffudd (died 1282). Isabella's father was evidently an adherent of Robert Bruce V, Lord of Annandale (died 1295), a man who staked a claim to the Scottish throne. The close relationship between the Domhnall's family and the Bruces is evidenced by two marriages. One was that between Isabella and Robert Bruce VII, Earl of Carrick (died 1329), a grandson of Robert Bruce V. Domhnall's son and comital successor, Gartnait (died c.1302), married a sister of Robert Bruce VII.
The marriage of Robert Bruce VII and Isabella probably took place in the 1290s. The union produced a single child, a daughter named Marjorie (died 1316), who was born in about 1296.
Following Isabella's death, Robert Bruce VII married his second wife, Elizabeth de Burgh (died 1327). Isabella's daughter, Marjorie, married Walter Stewart, Steward of Scotland, and their son eventually reigned as Robert II, King of Scotland (died 1390).