What is the largest moon in the solar system?

Ganymede is a natural satellite of Jupiter and is the largest and most massive moon in the Solar System. Like Saturn's largest moon, Titan, it is larger than the planet Mercury, but has somewhat less surface gravity than Mercury, Io, or Earth's Moon due to its lower density compared to the three. Ganymede orbits Jupiter in roughly seven days and is in a 1:2:4 orbital resonance with the moons Europa and Io, respectively.