Maeshowe (or Maes Howe; Old Norse: Orkahaugr) is a Neolithic chambered cairn and passage grave situated on Mainland Orkney, Scotland. It was probably built around 2800 BC. In the archaeology of Scotland, it gives its name to the Maeshowe type of chambered cairn, which is limited to Orkney.

Maeshowe is a significant example of Neolithic craftsmanship and is, in the words of the archaeologist Stuart Piggott, "a superlative monument that by its originality of execution is lifted out of its class into a unique position." Maeshowe is designated a scheduled monument and part of the "Heart of Neolithic Orkney", a group of sites including Skara Brae designated a UNESCO World Heritage Site in 1999.

Maeshowe is one of the largest tombs in Orkney; the mound encasing the tomb is 115 feet (35 m) in diameter and rises to a height of 24 feet (7.3 m). Surrounding the mound, at a distance of 50 feet (15 m) to 70 feet (21 m) is a ditch up to 45 feet (14 m) wide. The grass mound hides a complex of passages and chambers built of carefully crafted slabs of flagstone weighing up to 30 tons. It is aligned so that the rear wall of its central chamber is illuminated on the winter solstice. A similar display occurs in Newgrange.

This entrance passage is 36 feet (11 m) long and leads to the central almost square chamber measuring around 15 feet (4.6 m) on each side. The current height of the chamber is 12.5 feet (3.8 m), this reflects the height to which the original stonework is preserved and capped by a modern corbelled roof. The original roof may have risen to a height of 15 feet (4.6 m) or more. The entrance passage is only around 3 feet (0.91 m) high, requiring visitors to stoop or crawl into the central chamber. That chamber is constructed largely of flat slabs of stone, many of which traverse nearly the entire length of the walls. In each corner lie huge angled buttresses that rise to the vaulting. At a height of around 3 feet (0.91 m), the wall's construction changes from the use of flat to overlapping slabs creating a beehive-shaped vault.

Estimates of the amount of effort required to build Maeshowe vary; a commonly suggested number is 39,000 man-hours, although Colin Renfrew calculated that at least 100,000 hours would be required. Dating of the construction of Maeshowe is difficult but dates derived from burials in similar tombs cluster around 3000 BC. Since Maeshowe is the largest and most sophisticated example of the Maeshowe "type" of tomb, archaeologists have suggested that it is the last of its class, built around 2800 BC. The people who built Maeshowe were users of grooved ware, a distinctive type of pottery that spread throughout the British Isles around 3000 BC.

Maeshowe appears as a grassy mound rising from a flat plain near the southeast end of the Loch of Harray. The land around Maeshowe at its construction probably looked much as it does today: Treeless, with grasses representative of ‘pollen assemblage zone’ MNH-I, reflecting "mixed agricultural practices, probably with a pastoral bias – there is a substantial amount of ribwort pollen, but also that of cereals."

Maeshowe is aligned with some other Neolithic sites in the vicinity, for example, the entrance of "Structure 8" of the nearby Barnhouse Settlement directly faces the mound. In addition, the so-called "Barnhouse Stone" in a field around 700 metres away is perfectly aligned with the entrance to Maeshowe. This entrance corridor is so placed that it lets the direct light of the setting sun into the chamber for a few days on each side of the winter solstice, illuminating the entrance to the back cell.

A Neolithic "low road" connects Maeshowe with the magnificently preserved village of Skara Brae, passing near the Standing Stones of Stenness and the Ring of Brodgar. Low roads connect Neolithic ceremonial sites throughout Britain. Some archeologists believe that Maeshowe was originally surrounded by a large stone circle. The complex including Maeshowe, the Ring of Brodgar, the Standing Stones of Stenness, Skara Brae, as well as other tombs and standing stones represents a concentration of Neolithic sites that is rivalled in Britain only by the complexes associated with Stonehenge and Avebury.