This document discusses anchorage, which refers to resistance to unwanted tooth movement during orthodontic treatment. It classifies anchorage as intraoral or extraoral, simple or compound, according to the teeth or jaws involved. Factors that affect anchorage include biological factors like tooth size and mechanical factors like friction. Means of increasing anchorage include extraoral traction, inclined bite planes, and palatal arches. Anchorage loss can be prevented by moving fewer teeth at a time and using more teeth for anchorage.