The Mohole project, embodying the idea of drilling through the crust of the ocean floor to penetrate the Earth's mantle, was launched 40 years ago in 1957. Since that time drilling for scientific purposes has yielded otherwise unobtainable information about the solid Earth and how the Earth has evolved. Drilling has also revealed how the rocks of the Earth record diverse and changing interactions with the hydrosphere, atmosphere, and biosphere. Since 1967, scientific drilling at sea has been concentrated in the International Ocean Drilling Program (ODP) and two predecessor programs. Scientific drilling on the continents, in contrast, generally has been carried out through national programs.