This book summarizes the geological knowledge accumulated on Afar in the last 60 years,demonstrating thatitis, and will remain, a real hot spot for geological and geophysical research.It providesinsights intotheEarth processes along diverging plate boundaries,thestudy of boththecontinental and oceanic lithosphere and underlying asthenosphere, and margins and transitions including magmatic, volcanic, tectonic, sedimentary, hydrothermal and geodynamic processes. The Afar triangle is a geological depression that developed where the Gulf of Aden, Red Sea and East African Rift Valley meet. It isconsideredto beone of theEarth systemsmost important mantle plumes. In 1967, when the first expedition was organized,there was littleinformation on the geology of the area, and even geographic base maps were lacking.However,the first satellite photographsfrom the Apollo and Gemini space missionsofferedacomplete picture of the Red Sea-Gulf of Aden region, providing a new vision of the Afar triangle. The book describesthe unique geologicalfeaturesthatmakeAfarthe only place in the world where an oceanic plate boundarywith all its successive stepsof development can be observed inthe openair. Italso presentsthe Afar triangle as one of the cradles of first, nowextinct hominids. The Middle Awash area contains sites of several fossil discoveries, such as the well-known Lucy. The hydrothermal processesin Afarprovideconditions suitable for the study of the most primitive forms of life (archaebacterial)and it is also one of thefewplaces wheresignificant quantities of telluric energy areavailable at the surface for geothermal development.Further,the area has economically interesting mineral depositsand illustrates a number of current climate change issues. In addition to providing geological information,the book showsthat Afar is an area where anindividualhuman population developed with its own language and culture,andwhich adapted to the rugged landscape and extremely dry and hot climate.It is a valuable resourcefor scientists and students,and also servesthe needs of the Afar nation,currently splitin three different countries as a result of recenthistoricalevents.