The Fountain of Neptune (Fontana di Nettuno) is a monumental civic fountain located in the eponymous square, Piazza Nettuno, next to Piazza Maggiore, in Bologna, Italy Its bronze figure of Neptune, extending his reach in a lordly gesture of stilling and controlling the waters, is an early work of Giambologna's maturity, completed about 1567.

An innovation of Giambologna's fountain designs is the fantastic and non-geometrical forms he gave to the basins into which water splashed and flowed, "curiously folded, bulging and elastic in form", as Rosalind Grippi remarked. The fountain is a model example of Mannerist taste of the courtly elite in the mid-sixteenth century: construction of the statue was commissioned by the Cardinal Legate of the city, Charles Borromeo, to symbolize the fortunate recent election of Borromeo's uncle as Pope Pius IV.

The work was designed by the Palermitan architect Tommaso Laureti in 1563, with an over-lifesize bronze of the god Neptune on the top, executed by Giambologna, who had submitted a model for the fountain of Neptune in Florence, but had lost the commission to Baccio Bandinelli. Before the fountain was built, an entire edifice was demolished to make space for it. The fountain was completed in 1565, and the Neptune was fixed in place within a couple of years.