  Starting from the 2001 Thomas Friedrich's work on Spin(9), we review some
interactions between Spin(9) and geometries related to octonions. Several
topics are discussed in this respect: explicit descriptions of the Spin(9)
canonical 8-form and its analogies with quaternionic geometry as well as the
role of Spin(9) both in the classical problems of vector fields on spheres and
in the geometry of the octonionic Hopf fibration. Next, we deal with locally
conformally parallel Spin(9) manifolds in the framework of intrinsic torsion.
Finally, we discuss applications of Clifford systems and Clifford structures to
Cayley-Rosenfeld planes and to three series of Grassmannians.
