Methods and devices are provided for attaching one or more ancillary devices to an endoscope. The ancillary device can be any device that is used in conjunction with endoscopic procedures, such as, by way of non-limiting example, an accessory channel, tube, or sleeve, an indwelling tube or feeding tube, and surgical tools such as graspers, snares, etc. The ancillary device(s) can be positioned adjacent to and along side an external surface of an insertion portion of an endoscope for inserting into a body lumen, and one or more attachment devices can be used to mate the ancillary device(s) to the endoscope at one or more attachment locations. In use, the attachment device(s) will allow the ancillary device to move in coordination with the endoscope, thus allowing the endoscope and the ancillary device(s) to be introduced and guided through a tortuous pathway. In certain exemplary embodiments, the attachment device(s) can be configured to prevent radial movement, i.e., twisting, of the ancillary device relative to the endoscope, yet allow axial sliding of the ancillary device relative to the endoscope.