The compass is a magnetometer used for navigation and orientation that shows direction in regards to the geographic cardinal points. The structure of a compass consists of the compass rose, which displays the four main directions on it: East (E), South (S), West (W) and North (N). The angle increases in the clockwise position. North corresponds to 0°, so east is 90°, south is 180° and west is 270°.

The history of the compass started more than 2000 years ago during the Han dynasty (202 BC – 220 AD). The first compasses were made of lodestone, a naturally magnetized stone of iron, in Han dynasty China. It was called the "South Pointing Fish" and was used for land navigation by the mid-11th century during the Song dynasty (960–1279 AD). Shen Kuo provided the first explicit description of a magnetized needle in 1088 and Zhu Yu mentioned its use in maritime navigation in the text Pingzhou Table Talks, dated 1111–1117. Later compasses were made of iron needles, magnetized by striking them with a lodestone. Magnetized needles and compasses were first described in medieval Europe by the English theologian Alexander Neckam (1157–1217 AD). The first literary description of a compass in Western Europe was recorded in around 1190 and in the Islamic world 1232. Dry compasses begin appearing around 1269 in medieval Europe and 1300 in the medieval Islamic world. This was replaced in the early 20th century by the liquid-filled magnetic compass.

Before the introduction of the compass, geographical position and direction at sea were primarily determined by the sighting of landmarks, supplemented with the observation of the position of celestial bodies. Other techniques included sampling mud from the seafloor (China), analyzing the flight path of birds, and observing wind, sea debris, and sea state (Polynesia and elsewhere). Objects that have been understood as having been used for navigation by measuring the angles between celestial objects were discovered in the Indus Valley site of Lothal. The Norse are believed to have used a type of sun compass to locate true north. On cloudy days, the Vikings may have used cordierite or some other birefringent crystal to determine the sun's direction and elevation from the polarization of daylight; their astronomical knowledge was sufficient to let them use this information to determine their proper heading. The invention of the compass made it possible to determine a heading when the sky was overcast or foggy, and when landmarks were not in sight. This enabled mariners to navigate safely far from land, increasing sea trade, and contributing to the Age of Discovery.

The compass was invented in China during the Han dynasty between the 2nd century BC and 1st century AD where it was called the "south-governor" (sīnán 司南) or "South Pointing Fish" (指南魚). The magnetic compass was not, at first, used for navigation, but for geomancy and fortune-telling by the Chinese. The earliest Chinese magnetic compasses were possibly used to order and harmonize buildings by the geomantic principles of feng shui. These early compasses were made with lodestone, a form of the mineral magnetite that is a naturally occurring magnet and aligns itself with the Earth's magnetic field. People in ancient China discovered that if a lodestone was suspended so it could turn freely, it would always point toward the magnetic poles. Early compasses were used to choose areas suitable for building houses, growing crops, and to search for rare gems. Compasses were later adapted for navigation during the Song dynasty in the 11th century.

Based on Krotser and Coe's discovery of an Olmec hematite artifact in Mesoamerica, radiocarbon dated to 1400–1000 BC, astronomer John Carlson has hypothesized that the Olmec might have used the geomagnetic lodestone earlier than 1000 BC for geomancy, a method of divination, which if proven true, predates the Chinese use of magnetism for feng shui by a millennium. Carlson speculates that the Olmecs used similar artifacts as a directional device for astronomical or geomantic purposes but does not suggest navigational usage. The artifact is part of a polished hematite bar with a groove at one end, possibly used for sighting. Carlson's claims have been disputed by other scientific researchers, who have suggested that the artifact is actually a constituent piece of a decorative ornament and not a purposely built compass. Several other hematite or magnetite artifacts have been found at pre-Columbian archaeological sites in Mexico and Guatemala.

A number of early cultures used lodestone so they could turn, as magnetic compasses for navigation. Early mechanical compasses are referenced in written records of the Chinese, who began using it for navigation "some time before 1050, possibly as early as 850." At present, according to Kreutz, scholarly consensus is that the Chinese invention used in navigation pre-dates the first European mention of a compass by 150 years. The first recorded appearance of the use of the compass in Europe (1190) is earlier than in the Muslim world (1232), as a description of a magnetized needle and its use among sailors occurs in Alexander Neckam's De naturis rerum (On the Natures of Things), written in 1190.

However, there are questions over diffusion. Some historians suggest that the Arabs introduced the compass from China to Europe. Some suggested the compass was transmitted from China to Europe and the Islamic world via the Indian Ocean, or was brought by the crusaders to Europe from China. However, some scholars have proposed an independent European invention of the compass.

These are noteworthy Chinese literary references in evidence for its antiquity: