Ortho

Ortho- is a Greek prefix meaning “straight”, “upright”, “right” or “correct”.

Ortho may refer to:
 * Ortho, Belgium, a village in the Belgian province of Luxembourg

Science

 * Arene substitution patterns, two substituents that occupy adjacent positions on an aromatic ring
 * Chlordane, an organochlorine compound that was used as a pesticide

Mathematics

 * Orthogonal, a synonym for perpendicular
 * Orthonormal, the property that a collection of vectors are mutually perpendicular and each of unit magnitude
 * Orthodrome, a synonym for great circle, a geodesic on the sphere
 * Orthographic projection, a parallel projection onto a perpendicular plane

Medicine

 * Orthomyxovirus, a family of viruses to which influenza belongs
 * Orthodontics, a specialty of dentistry concerned with the study and treatment of malocclusions
 * Orthopedic, the study of the musculoskeletal system
 * Ortho-DOT, a psychedelic drug
 * Ortho-cept and Ortho Tri-cyclen, kinds of oral contraceptive drug

Theology

 * Orthodoxy, right (correct) belief
 * Orthopraxy, right (correct) action

Business

 * Ortho Pharmaceutical, which merged into Ortho-McNeil Pharmaceutical before being bought by Johnson & Johnson
 * Ortho-Clinical Diagnostics, a subsidiary of Quidel Corporation
 * Ortho, a lawn care and pesticide company owned by the Scotts Miracle-Gro Company