The painting is a portrait of Ludovico it Moro's mistress Cecilia Gallerani and can be dated to between 1485 and 1490. The picture is also celebrated in a sonnet by the court poet Bernardo Bellincioni, who died in 1492, and so we can be certain that it had been executed by this date. In a letter sent by Cecilia Gallerani to Isabella d'Este in 1498, in response to Isabella's request for the painting, the woman declared that in the meantime her appearance had changed and she could no longer recognize herself in the portrait. According to some scholars, this suggests that the picture was painted when Gallerani was very young, and so should be dated to around 1485. This is corroborated by the comparison with a preparatory study for the Virgin of the Rocks, executed during the Da Vinci’s first stay in Milan, which presents surprising similarities to the face and pose of the Lady with an Ermine.
The animal has attracted more attention from scholars than Cecilia herself. Some believe that it is an allusion to Moro, who had received from the king of Naples, Ferrante of Aragon, the decoration of the order of St. Michael or of the Ermine. In a sonnet Bellincioni described Moro as "italico morel, bianco ermellino" ("dark Italian white ermine").
The link between Cecilia and the ermine, a symbol of chastity, appears more enigmatic: according to some it may lie in the assonance between her surname (Gallerani) and the Greek word for ermine, gale.
The composition of the portrait painting is extremely refined, based on the three-quarters position of the woman and the counterpoint of the ermine's movement. The handling of the forms is sure, and they are rendered even more evident by the choice of a dark background.