Clean energy technologies and systems for a sustainable world

This Special Issue contains a selection of papers from the proceedings of the Third International Conference on Applied Energy 2011, ICAE2011, which was held in Perugia, Italy from 16 to 18 May 2011. After the previous successful two ICAE conferences, which were held in Hong Kong and Singapore, Asia, the third one was the first organized in Europe. The theme of the conference was kept the same as the previous edition, ''Energy Solutions for a Sustainable World'', to show the continuity with the past and to confirm the need to continue our efforts to improve the performance of energy technologies and systems and to make energy conversion in all its forms more and more compatible with environmental protection and sustainable development.