Orthotics is the allied health science devoted to the design, fabrication, fitting, and management of supportive devices from head to toe. Orthotics provide external support or assist weak or abnormal joints and/or muscle groups. Musculoskeletal disorders, joint weakness, back problems, or the inability of any joint or muscle group to function correctly can greatly decrease people's activities of daily living. Congenital factors, degenerative disease, traumatic injury, chronic conditions, or sports injuries can cause these problems.

A person schooled in orthotics is called an orthotist. Orthotists are devoted to helping people with musculoskeletal disorders (weak or ineffective joints/muscles) by providing appropriate corrective, supportive, and, at times, assistive devices. Orthotists use biomechanical science to help reach this end. In many instances, it is necessary to design and fabricate a custom orthosis for a specific need. In others, the orthotist custom fits an off-the-shelf (OTS) device to the patient to achieve the desired results. The orthotist along with his/her technicians perform adjustments, repairs, and realignments as necessary throughout the life of the orthotic.

An orthosis may be worn temporarily until a weakness or injury is overcome, or on a permanent basis to aid impaired function due to a congenital or degenerative condition.