Camilla Martelli (c. 1545 – 30 May 1590) was first the lover and then the second wife of Cosimo I de' Medici, Grand Duke of Tuscany.

Camilla stood by him during his middle age, when because of his poor health he retired to private life in the villa di Castello, abdicating in favour of his son Francesco I de' Medici.

They did not agree with her appetite for ostentatious luxury, which appeared vulgar in comparison to the tasteful elegance of his late wife Eleonora of Toledo.

In 1574 Cosimo I, who had had at least one stroke, had limited mobility and was unable to speak due to circulatory problems; he died on 30 April.

Eager to enjoy greater freedom after the death of Francesco I, she asked Grand Duke Ferdinando I to let her leave the convent.