Adelard (Athelard) of Bath was a 12th century English scholar. He is best known for translating many important Arabic scientific works of astrology, astronomy, philosophy and mathematics into Latin, including ancient Greek texts which only existed in Arabic form, which were then introduced to Europe. During a period of seven years he travelled throughout North Africa and Asia Minor. He studied at Tours and may have taught at Laon. There is some dispute over the latter (Burnett 1987).

His best known work is that of his Arabic studies, including those of , collected under the title of Perdifficiles Quaestiones Naturales (Natural Questions), first mass printed in 1472, in the form of a dialogue between himself and a nephew between 1113 to 1133. In Natural Questions he displays some original thought of a scientific bent, raising the question of the shape of the Earth (he believed it round) and the question of how it remains stationary in space, and also the interesting question of how far a rock would fall if a hole were drilled through the earth and a rock dropped in it, see center of gravity. He theorized that matter could not be destroyed, see Law of conservation of matter. Also the interesting question of why water experiences difficulty flowing out of a container that has been turned upside down, see atmospheric pressure and vacuum. Many of the other questions addressed reflect the popular culture of the times.

He translated the Kharismian Tables and an Arabic Introduction to Astronomy. He wrote a short treatise on the abacus (Regulae abaci). He wrote a treatise on the astrolabe. He translated Euclid's Elements into Latin from an Arabic translation of the Greek original. Johannes Campanus probably had access to Adelard's translation of Elements, and it is Campanus' edition that was first published in Venice in 1482 after the invention of the printing press. It became the chief text-book of the mathematical schools of Europe.