A selection of key findings from a five-year research study of Decision-Making in the Planning, Appraisal and Delivery of Mega Transport Projects (MTPs): Lessons for Decision-makers (OMEGA 2 Study) is presented in this executive summary. An international study of 30 selected Mega Transport Projects (MTPs) completed since 1990 in Europe, USA, Australia and Asia-Pacific provided the focus of this research. A definition of MTPs is important, for the purpose of this research, as land-based transport infrastructure investments connecting and within major urban areas and metropolitan regions in the form of tunnels, bridges, rail and road links, or combinations of all of the above. MTPs are projects that entail the following: a construction cost of over US$1 billion (at 1990 prices), completion since 1990; and frequently perceived as critical to the success of major urban, metropolitan, national and/or regional development. What constitutes a ‘successful’ MTP, in light of the aims of such projects and the anticipated challenges presented by the 21st century is the overarching research question posed by the OMEGA 2 Study. Going well beyond the conventional project management concerns of on-time project completion, remaining on-budget, and staying within prescribed specification, often referred to as ‘Iron Triangle” considerations of project management, these considerations remain important to this investigation, nonetheless.