Apparatus and methods are provided for forming a gastrointestinal tissue fold by engaging tissue at a first tissue contact point and moving the first tissue contact point from a position initially distal to, or in line with, a second tissue contact point to a position proximal of the second contact point, thereby forming the tissue fold, and extending an anchor assembly through the tissue fold from a vicinity of the second tissue contact point. Adjustable anchor assemblies; as well as anchor delivery systems, shape-lockable guides and methods for endoluminally performing medical procedures, such as gastric reduction, treatment of gastroesophageal reflux disease, resection of lesions, and treatment of bleeding sites; are also provided.