The crystallization processes in polymer blends and the subsequent morphology and crystal structures formed are of great interest because of their significance, especially in the determination of their performance properties. Therefore, in this chapter, the fundamentals of crystallization in polymers were discussed first and then related to the real situation in polymer blends with nanoparticles. Fractionated crystallization phenomenon was thoroughly looked into as it relates to dispersed phase and confined domain. Nanostructured polymer blends present a not too different scenario when compared to the neat polymers, but still, their crystallization processes offer something to talk about. In addition, the polymorphic development in immiscible blends was also a subtopic that was discussed. In all, an adequate amount of literature was referred to.