Maria Gaetana Agnesi (16 May 1718 – 9 January 1799) was a Milanese mathematician, philosopher, theologian, and humanitarian. She was the first woman to write a mathematics handbook, the first woman appointed as a mathematics professor at a university and the second woman appointed as a professor overall.

She is credited with writing the first book discussing both differential and integral calculus and was a member of the faculty at the University of Bologna, although she never served.

She devoted the last four decades of her life to studying theology (especially patristics) and to charitable work and serving the poor. She was a devout Catholic and wrote extensively on the marriage between intellectual pursuit and mystical contemplation, most notably in her essay Il cielo mistico (The Mystic Heaven). She saw the rational contemplation of God as a complement to prayer and contemplation of the life, death and resurrection of Jesus Christ.

Maria Teresa Agnesi Pinottini, harpsichordist and composer, was her sister.

Maria Gaetana Agnesi was born in Milan, to a wealthy and literate family. Her father Pietro Agnesi, a wealthy silk merchant, wanted to elevate his family into the Milanese nobility. In order to achieve his goal, he married Anna Fortunato Brivio of the Brivius de Brokles family in 1717. Her mother's death provided her the excuse to retire from public life. She took over the management of the household. She was one of 21 children.

Maria was recognized early on as a child prodigy; she could speak both Italian and French at five years of age. At the age of nine, she composed and delivered a speech arguing for the education of women. By her eleventh birthday, she had also learned Greek, Hebrew, Spanish, German, and Latin, and was referred to as the "Seven-Tongued Orator".

Agnesi suffered a mysterious illness at the age of twelve that was attributed to her excessive studying and reading, so she was prescribed vigorous dancing and horseback riding. This treatment did not work; she began to experience extreme convulsions, after which she was encouraged to pursue moderation. By age fourteen, she was studying ballistics and geometry. When she was fifteen, her father began to regularly gather in his house a circle of the most learned men in Bologna, before whom she read and maintained a series of theses on the most abstruse philosophical questions. Records of these meetings are given in Charles de Brosses' Lettres sur l'Italie and in the Propositiones Philosophicae, which her father had published in 1738 as an account of her final performance, where she defended 190 philosophical theses.

Her father remarried twice after Maria's mother died, and Maria Agnesi ended up the eldest of 21 children, including her half-siblings. Her father agreed with her that if she were to continue her mathematics research, then she would be permitted to do all the charity work she wanted. In addition to her performances and lessons, her responsibility was to teach her siblings. This task kept her from her own goal of entering a convent, as she had become strongly religious. Although her father refused to grant this wish, he agreed to let her live from that time on in an almost conventual semi-retirement, avoiding all interactions with society and devoting herself entirely to the study of mathematics. After having read in 1739 the Traité analytique des sections coniques of the Marquis Guillaume de l'Hôpital, she was fully introduced into the field in 1740 by Ramiro Rampinelli, an Olivetan monk who was one of the most notable Italian mathematicians of that time. During that time, Maria studied with him both differential and integral calculus.