Deep soil organic carbon (SOC) represents a substantial component of terrestrial carbon stocks, yet its distribution and persistence remain poorly understood, particularly in African soil–landscape systems. This seminar will present evidence from the Ethiopian Highlands, drawing on more than 112 deep soil profiles extending to approximately 200 cm. I will examine how SOC stocks vary with depth, soil type, clay content, and landscape position, and consider the processes that may control carbon storage below the conventional 30-cm sampling depth. I will then discuss the roles of mineral association, carbon supply, microbial processing, hydrology, and pedogenesis, and consider the implications for deep-SOC prediction and process-based modelling. The seminar will conclude with opportunities for UK–Ethiopia collaboration to better understand deep-SOC persistence and vulnerability under environmental change.