This document discusses anchorage in orthodontics. It defines anchorage as the resistance to unwanted tooth movement. It classifies anchorage according to site (intraoral vs extraoral), number of units (simple vs compound), and arch form (Moyers and Burstone classifications). Biological factors like tooth morphology and muscles affect anchorage. Mechanically, friction influences anchorage. The document reviews anchorage considerations for removable and fixed appliances historically used like edgewise and Begg appliances. It also discusses anchorage preparation and loss.