This document on ISDN field trial guidelines has been prepared specifically to provide help and guidance to those countries wishing to initiate ISDN field trials. The document calls on the experience already gained through existing ISDN installations to provide the necessary background and information. Additionally many countries have already progressed towards integrated digital switching and transmission for voice networks, (commonly referred to as IDN) as a necessary precursor to the introduction of ISDN. The primary purpose of the field trial guidelines handbook is to support development of planning and implementation requirements necessary for the conduct of a successful ISDN trial, including evaluation of the results.