Composite Materials are subject to a wide variety of damage modes. The most common damage modes are intralaminar cracking, delamination or interlaminar cracking, debonding fiber-matrix, and finally fiber breakage. All damage modes cause mechanical properties reduction. This is the case of intralaminar cracks, which are studied in this work. First, this research sets the matrix cracking problem of a composite laminate in terms of Fracture Mechanics throughout the introduction of the in-situ strength theory. Then, a damage model (Discrete Damage Model, DDM) characterized by being formulated exclusively in terms of crack density and fracture toughness is presented. This model is compared to experimental results in order to obtain the material properties that govern the matrix cracking response. These properties are fracture toughness in modes I and II. ____________________________________________________________________________________________________________________-