Olduvai is one of the most important prehistoric sites in the world; indeed, the only Middle Pleistocene site of comparable importance is Choukoutien and Olduvai can show deposits far older. The site has produced a mass of material of the highest archaeological and palaeontology importance and in this first of five volumes Dr Leakey and his collaborators make their preliminary reports. The story of the excavations initiated by Dr Leakey in 1951 is well known. Their purpose was to locate and uncover a series of living-floors of early Hand-axe man and, if possible, of the preceding Olduwan culture. The discoveries were of striking and far-reaching importance. They included, besides a mass of tools and artefacts, small animal and human remains and the famous skull of Zinjanthropus boisei, the earliest tool-making man. Against this background Leakey and his collaborators discuss the geological evidence, its relation to the fauna and other fossil evidence, the problems of climatic sequence and the use of potassium-argon dating.