The seismically and volcanically active East African Rift System is an ideal laboratory for continental break-up processes: it encompasses all stages of rift development. Its northernmost sectors within the Afar volcanic province include failed rifts, nascent sea-floor spreading, and youthful passive continental margins associated with one or more mantle plumes. A number of models have been proposed to explain the success and failure of continental rift zones, but there remains no consensus on how strain localizes to achieve rupture of initially 125-250 km-thick plates, or on the interaction between the plates and asthenospheric processes. This collection of papers provides new structural, stratigraphic, geochemical and geophysical data and numerical models needed to resolve fundamental questions concerning continental break-up and mantle plume processes. The focus is on how mantle melt intrudes and is distributed through the plate, and how this magma intrusion process controls along-axis segmentation and facilitates break-up.