Parts 1,2 and 3 available here.This publication contains the papers presented at the 15th European Conference on Soil Mechanics and Geotechnical Engineering ECSMGE, held in Athens, Greece. Considerable progress has been made in recent decades in understanding the engineering behavior of those hard soils and weak rocks that clearly fall into either the field of soil or of rock mechanics, and there have been important developments in design and construction methods to cope with them. Progress would be even more desirable, however, for those materials which fall into the grey area between soils and rocks. They present particular