Finite Elements Analysis in the setting of Fracture Mechanics is a topic that engineers, mathematics and physics frequently face. In this book we describe crack-microcrack interactions in theoretical and numerical way proposing a multi-field scheme for elastic microcracked bodies and its discretization in presence of macroscopic cracks. We start reviewing the basic laws of crack propagation in Cauchy's Continuua and show numerical schemes based on Finite Element Methods (FEM) and eXtended Finite Element Methods (XFEM). The reading of this book is suggested for students and researchers who are interested in mathematical modelling and numerical computation of cracking phenomena. The content of this book was awarded during the European Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS 2004, Jyvaskyla, Finland, 24 - 28 July 2004."