The development of the modern industry has increased the demand for polycrystal models with high prediction capability. Crystal Plasticity (CP) is one of the advanced modeling solutions owing to its multi-scale nature and the capability to quantify precisely the effects of directional deformation mechanisms. In this article, CP modeling is introduced including its original theory and extension to twinning and dislocation climb. The CP-based polycrystal modeling techniques at different length-scales are also summarized. In addition, the recent advancements in CP modeling are briefly reviewed, with a discussion of the future development in this field.