After sketching the nature of perturbative strings and the discovered dualities, I review the Discrete Light Cone Quantization and Seiberg's derivation of the Susskind & Motl's DLCQ description of M-theory using the Matrix model of Banks, Fischler, Shenker and Susskind. Then I discuss the appearance of multiparticle states and matrix strings in the picture. Finally I show the novelties arising when the DLCQ treatment is used for heterotic models with 16 supersymmetries.