Masaya is a large basaltic shield volcano located 20 km south of Managua, Nicaragua, Central America and is Nicaragua's first and largest National Park. The volcanic complex is composed of a nested set of calderas and craters, the largest of which is Las Sierras shield and caldera. Within this caldera lies Masaya Volcano sensu stricto, a shallow shield composed of basaltic lavas and tephras. This hosts Masaya caldera, formed 2500 years ago by an 8-km3 basaltic ignimbrite eruption. Inside this caldera a new basaltic complex has grown from eruptions mainly on a semi-circular set of vents that include the Masaya and Nindiri cones. The latter host the pit craters of Masaya, Santiago, Nindiri and San Pedro. Observations in the walls of the pit craters indicate that there have been several episodes of cone and pit crater formation.

The floor of Masaya caldera is covered by poorly vegetated lavas, indicating resurfacing within the past 1000 or so years, but only two lava flows have erupted since the sixteenth century. The first, in 1670, was an overflow from the Nindiri pit, which at that time hosted a 1-km-wide lava lake. The other, in 1772, issued from a fissure on the flank of the Masaya cone. Since 1772, lava has appeared at the surface only in the Santiago pit crater (presently active and persistently degassing) and possibly within Nindiri crater in 1852.

During the rainy season, it is common for rainwater to percolate into the volcano, causing it to emit lots of acidic steam. The population of Masaya is of about 150,000 people of mostly indigenous, German or Spanish ancestry, and the only city in Pacific and Mountainous Nicaragua with the highest unmixed indigenous population.