Alba Mons (formerly and still occasionally known as Alba Patera, a term that has since been restricted to the volcano's summit caldera; also initially known as the Arcadia ring) is a volcano located in the northern Tharsis region of the planet Mars. It is the biggest volcano on Mars in terms of surface area, with volcanic flow fields that extend for at least 1,350 km (840 mi) from its summit. Although the volcano has a span comparable to that of the United States, it reaches an elevation of only 6.8 km (22,000 ft) at its highest point. This is about one-third the height of Olympus Mons, the tallest volcano on the planet. The flanks of Alba Mons have very gentle slopes. The average slope along the volcano's northern (and steepest) flank is 0.5°, which is over five times lower than the slopes on the other large Tharsis volcanoes. In broad profile, Alba Mons resembles a vast but barely raised welt on the planet's surface. It is a unique volcanic structure with no counterpart on Earth or elsewhere on Mars.

In addition to its great size and low relief, Alba Mons has a number of other distinguishing features. The central portion of the volcano is surrounded by an incomplete ring of faults (graben) and fractures, called Alba Fossae on the volcano's western flank and Tantalus Fossae on the eastern flank. The volcano also has very long, well preserved lava flows that form a radiating pattern from the volcano's central region. The enormous lengths of some individual flows (>300 km (190 mi)) implies that the lavas were very fluid (low viscosity) and of high volume. Many of the flows have distinctive morphologies, consisting of long, sinuous ridges with discontinuous central lava channels. The low areas between the ridges (particularly along the volcano's northern flank) show a branching pattern of shallow gullies and channels (valley networks) that likely formed by water runoff.

Alba Mons has some of the oldest extensively exposed volcanic deposits in the Tharsis region. Geologic evidence indicates that significant volcanic activity ended much earlier at Alba Mons than at Olympus Mons and the Tharsis Montes volcanoes. Volcanic deposits from Alba Mons range in age from Hesperian to early Amazonian (approximately 3.6 to 3.2 billion years old).

For years the volcano's formal name was Alba Patera. Patera (pl. paterae) is Latin for a shallow drinking bowl or saucer. The term was applied to certain ill-defined, scalloped-edged craters that appeared in early spacecraft images to be volcanic (or non-impact) in origin. In September 2007, the International Astronomical Union (IAU) renamed the volcano Alba Mons (Alba Mountain), reserving the term Alba Patera for the volcano's two central depressions (calderas). Nevertheless, the entire volcano is still commonly called Alba Patera in the planetary science literature.

The term Alba is from the Latin word for white and refers to the clouds frequently seen over the region from Earth-based telescopes. The volcano was discovered by the Mariner 9 spacecraft in 1972 and was initially known as the Alba volcanic feature or the Arcadia Ring (in reference to the partial ring of fractures around the volcano). The IAU named the volcano Alba Patera in 1973. The volcano is often simply called Alba when the context is understood.

Alba Mons is centered at 40°28′N 250°24′E / 40.47°N 250.4°E / 40.47; 250.4 in the Arcadia quadrangle (MC-3). Much of the volcano's western flank is located in the adjacent Diacria quadrangle (MC-2). Flows from the volcano can be found as far north as 61°N and as far south as 26°N (in the northern Tharsis quadrangle). If one takes the outer margin of the flows as the volcano's base, then Alba Mons has north–south dimensions of about 2,000 km (1,200 mi) and a maximum width of 3,000 km (1,900 mi). It covers an area of at least 5.7 million km² and has a volume of about 2.5 million km³. The volcano dominates the northern portion of the Tharsis bulge and is so large and geologically distinct that it can almost be treated as an entire volcanic province unto itself.

Although Alba Mons reaches a maximum elevation of 6.8 km (22,000 ft) above Mars’ datum, the elevation difference between its summit and surrounding terrain (relief) is much greater on the north side of the volcano (about 7.1 km (23,000 ft)) compared to the south side (about 2.6 km (8,500 ft)). The reason for this asymmetry is that Alba straddles the dichotomy boundary between the cratered uplands in the south and the lowlands to the north. The plains underlying the volcano slope northward toward the Vastitas Borealis, which has an average surface elevation of 4.5 km (15,000 ft) below datum (-4.500 km (14,760 ft)). The southern part of Alba Mons is built on a broad, north–south topographic ridge that corresponds to the fractured, Noachian-aged terrain of Ceraunius Fossae (pictured left).

Alba's size and low profile makes it a difficult structure to study visually, as much of the volcano's relief is indiscernible in orbital photographs. However, between 1997 and 2001, the Mars Orbital Laser Altimeter (MOLA) instrument of the Mars Global Surveyor spacecraft took over 670 million precise elevation measurements across the planet. Using MOLA data, planetary scientists are able to study subtle details of the volcano's shape and topography that were invisible in images from earlier spacecraft such as Viking.