This publication emphasizes the integrity and interdependence of various activities related to invitation of bids, their technical and economic evaluation, and contracting. It updates information included in existing IAEA publications in order to better reflect the developments in the nuclear and energy industry, and constitutes a compact and user friendly guidebook integrating the existing IAEA publications on the subject. It provides the information necessary to organize, guide and realize the activities related to the invitation of bids, their technical and economic evaluation, and contracting as an integrated process. Furthermore, this publication indicates how and to what degree the activities preceding the preparation of the bid invitation specification, the evaluation of bids and contracting can influence the process.