This Special Issue (n. 165 of the International Journal Engineering Geology) collects a review of the most recent developments in the mechanics of unsaturated soils, and a perspective on geological, geo-environmental and geotechnical problems to which unsaturated soil mechanics provides a comprehensive framework. The papers included in the Issue are the written version of the invited contributions to the Second European Conference on Unsaturated Soils, E-UNSAT 2012, held in Napoli, Italy, on June 2012. The conference was supported by the Technical Committee 106 - Unsaturated Soils of the International Society of Soil Mechanics and Geotechnical Engineering. The twelve papers address the three thematic areas Experimental, Modelling, and Engineering, in which the contemporary activity may be broadly encompassed, and is intended to provide a valuable up-to-date reference across the subject for both researchers and practitioners.