A brief overview; projective geometries; beginning derivation; spreads; derivable nets; the Hughes planes; Desarguesian planes; Pappian planes; characterizations of geometries; derivable nets and geometries; structure theory for derivable nets; dual spreads and Baer subplanes; derivation as a geometric process; embedding; classification of subplane covered nets; subplane covered affine planes; direct products; parallelisms; partial parallelisms with deficiency; Baer extensions; translation planes admitting Baer groups; spreads covered by pseudo-Reguli; conical and ruled planes over fields; spreads which are dual spreads; partial flocks of deficiency one; Skew-Hall planes.