Widespread tephra horizons, typically resulting from ash fallout from large volcanic eruptions, have the potential to form excellent isochronous marker horizons across diverse depositional environments. This provides the opportunity to use well-characterised tephra horizons as marker horizons to synchronise sedimentary archives studied for a variety of applications, including volcanology, archaeology, palaeontology, palaeoclimatology, palaeoecology and palaeoseismology. In East Africa, tephrochronology has been successfully applied in multiple disciplines, and on varying timescales: from regional-scale synchronisation and dating of hominin sites, to more focused studies of the Late Quaternary eruptive history of specific, potentially active, volcanoes. In this session we invite contributions from various scientific disciplines using tephra as a geochronological tool, particularly in East Africa.  We especially welcome ideas on how to tackle the challenges that may exist in the various applications of tephrochronology, e.g. technical challenges in absolute dating or analysing chemical composition, identifying source volcanoes, distinguishing between multiple eruptions from the same source, distinguishing primary from secondary reworked tephra, etc. We are confident this session should stimulate discussion across a range of disciplines and applications.