This document provides definitions and descriptions of various hip, knee, ankle, and foot orthoses. It describes a hip-knee-ankle-foot orthosis (HKAFO) as an orthosis that stabilizes or locks the hip, knee, and ankle. The typical HKAFO consists of two knee-ankle-foot orthoses linked above the hip with a pelvic band or lumbosacral orthosis. It also discusses indications, principles, components, and fabrication of HKAFOs as well as other orthoses like reciprocal gait orthoses and hip orthoses.