Starting from the 2001 Thomas Friedrich’s work on $\mathrm{Spin}\left(9\right)$ , we review some interactions between $\mathrm{Spin}\left(9\right)$ and geometries related to octonions. Several topics are discussed in this respect: explicit descriptions of the $\mathrm{Spin}\left(9\right)$ canonical 8-form and its analogies with quaternionic geometry as well as the role of $\mathrm{Spin}\left(9\right)$ 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 $\mathrm{Spin}\left(9\right)$ 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.