A megaproject is an extremely large-scale investment project. The European Cooperation in Science and Technology (COST) categorises megaprojects as having "extreme complexity (both in technical and human terms) and by a long record of poor delivery". Megaprojects attract a lot of public attention because of substantial impacts on communities, environment, and budgets, and many cost more than US$1 billion. Megaprojects can also be defined as "initiatives that are physical, very expensive, and public". Bent Flyvbjerg, a professor at the Saïd Business School of the University of Oxford says that globally, megaprojects make up 8 percent of total GDP.

Care in the project development process is required to reduce any possible optimism bias and strategic misrepresentation, as a curious paradox exists in which more and more megaprojects are being proposed despite their consistently poor performance against initial budget and schedule forecasts.

Examples

Megaprojects include bridges, tunnels, highways, railways, airports, seaports, power plants, dams, wastewater projects, Special Economic Zones, oil and natural gas extraction projects, public buildings, information technology systems, aerospace projects, weapons systems, large-scale sporting events and, more recently, mixed use waterfront redevelopments; however, the most common megaprojects are in the categories of hydroelectric facilities, nuclear power plants, and large public transportation projects.