Transmission planning in a restructured electricity market becomes increasingly complicated. To bridge the gap between economic and engineering considerations, this survey paper suggests a framework to clarify the interactions among various economic and engineering issues by reviewing recent theoretical and practical progress in transmission investment and transmission planning methodology. Thus, the paper makes economic literature more accessible to the engineering community and engineering literature more accessible to the economic community interested in the subject. (C) 2005 Elsevier Ltd. All rights reserved.