A steerable overtube is provided having an elongate shaft comprising an oversized accessory channel that is configured for the introduction and advancement of elongate medical devices having relatively large cross-sections. The distal end of the overtube shaft is bendable or deflectable in at least one direction, and is preferably includes a shape locking mechanism for temporarily maintaining the shape of the distal end of the overtube shaft. An oversized accessory channel is provided. The overtube may also include a fixation mechanism for securing the proximal end and/or distal end of the overtube against movement relative to the patient. A fiber optic elongate medical device is provided for use with the steerable overtube of the present invention.
