Giovanni Battista Agucchi (20 November 1570 – 1 January 1632) was an Italian churchman, Papal diplomat and writer on art theory. He was the nephew and brother of cardinals, and might have been one himself if he had lived longer. He served as secretary to the Papal Secretary of State, then the Pope himself, on whose death Agucchi was made a titular bishop and appointed as nuncio to Venice. He was an important figure in Roman art circles when he was in the city, promoting fellow-Bolognese artists, and was close to Domenichino in particular. As an art theorist he was rediscovered in the 20th century as having first expressed many of the views better known from the writings of Gian Pietro Bellori a generation later. He was also an amateur astronomer who corresponded with Galileo.