This is the first book that systemically introduces the theory and implementation of Computational Grains for micromechanical modeling of heterogeneous materials. This book covers the specifically designed mathematics embedded in Computational Grains, and the entire process of microstructure construction, tessellation, CG simulation and homogenization. The Computational Grains discussed in this book consider elastic, non-elastic, and multi-physics solids. Materials damage development are also preliminarily discussed, with CGs considering matrix-inclusion debonding as well as embedded microcracks. Presenting the theory step-by-step and with detailed examples and MATLAB codes, the material is accessible and practical for readers. This will be ideal for graduate students and researchers in mechanical and aerospace engineering and applied mechanics.