The main features of diffractive processes and QCD inspired models are overviewed. The following topics are discussed: (1) Diagonal (elastic) diffraction, which shows that the underlying theory is non-abelian;
(2) Quantum mechanics and general features of the off-diagonal diffractive processes; (3) Color dipole description of diffraction; (4) triple-Regge phenomenology; (5) what do we learn about hadron structure from soft diffraction? Why interaction of Pomerons is so weak?
(6) Diffraction near the unitarity bound: why the diffractive cross stops rising;
(7) “Hard diffraction” turns out to be semisoft-semihard;
(8) factorization of short- and long-distance interactions is severely broken in hard diffractive hadronic collisions;
(9) examples: diffractive DIS, diffractive Drell-Yan, diffractive production of gauge bosons, diffractive heavy flavors, diffractive Higgs production.