  These are notes of lectures given at the Third School of Theoretical Physics
in Jijel (Algeria, September 2009). The subject of these notes is differential
geometry, complex and quaternionic structures with applications to theoretical
physics. Concerning the physical applications, they contain several aspects of
Penrose transformation in the Riemannian context (Euclidean signature) and
various formulations of the Yang-Mills and Einstein equations among which
several are unusual ones.
