Isabella I (1172 – 5 April 1205) is Queen regnant of Jerusalem from 1190/1192 until her death.

By her four marriages, she is successively Lady of Toron, Marchioness of Montferrat, Countess of Champagne and Queen of Cyprus.

Sheis the daughter of Amalric I of Jerusalem and his second wife Maria Comnena, making her a younger half-sister of King Baldwin IV of Jerusalem and Queen Sibylla of Jerusalem.

She is also the aunt of Baldwin V, and a grandniece of Byzantine emperor Manuel I Comnenus, who had received the town and territory of Nablus as a dower from her husband the king.

She marries four times.

Maria of Montferrat, Queen of Jerusalem, is her daughter by her second husband, Conrad of Montferrat.

She has a total of seven children by her various husbands.

Isabella I has been conjectured as the possible identity of the 13th-century trobairitz known only as Ysabella.