This lecture will provide some background on the geometry of 8-dimensional Riemannian manifolds with holonomy Spin(7). The talk is part of a series of lectures on the geometry of Riemannian manifolds with holonomy Spin(7) during the week Nov 24-28. The event is part of the activities of the FIS2 project BeyondCY3. More information available at: https://sites.google.com/uniroma1.it/lfoscolo/fis2-beyondcy3/events