MATRIX MODELS, TOPOLOGICAL FIELD-THEORIES AND C-LESS-THAN-OR-EQUAL-TO-1 STRING THEORY

We review ordinary and extended two-matrix models and their applicatio n to 2D gravity. After a general introduction we deal in particular wi th two aspects: 1) the emergence from two-matrix models of n-th KdV hi erarchies and the topological field theories associated to them; 2) th e representation of the discrete states of the c=1 string theory by me ans of the extended two-matrix model. These constitute two remarkable examples of our idea that two-matrix models provide a unifying descrip tion of 2D gravity coupled to c less than or equal to 1 conformal matt er.