Mary Beale (1633–1699) was the most important of the handful of women who can be regarded as the first in Britain to have conducted professional careers as artists. For over four decades she operated as a portrait painter in London, working from her home and studio in Pall Mall. From the wealth of documentation about her that survives, including annual notebooks kept by her husband, a detailed picture can be gained of her painting practice and her husband’s role as studio manager, as well as the London art world in general and her social milieu. What is less known about her is her writing. In her discourse on friendship, written in 1667, she makes a robust argument for women’s equality with men through friendship in marriage. The context for her thoughts is the religious outlook of her family and circle of friends that included leading latitudinarian Anglican churchmen such as John Tillotson, to whose wife, Elizabeth, Beale dedicated her discourse. For Beale, friendship was a code of conduct that she applied to her life, that she enjoyed in her own marriage, that can be witnessed in the interactions of her mutually supportive circle, and that can also be observed in her paintings.