Retrosynthetic analysis, first developed decades ago, plans the synthetic routes of pharmaceuticals and industrial chemicals by transforming a target molecule into simpler precursors until available building block molecules are reached. Computer assisted synthesis planning (CASP) has gained great interests since it accelerates the development of retrosynthetic routes. The emergence of chemical reaction databases and the ability to mine data from historical literature and patents made it possible for the development of numerous data-driven CASP methods. Recent successes in this field include: (i) generation of reaction networks based on graph theory, using vertices to represent molecules and directed edges to represent reactions from reactants to products, to understand connectivity among molecules, (ii) manual curation and algorithmic extraction of reaction rules and templates from historical reactions to predict functional group transformations, (iii) template-free deep learning methods to learn from historical reactions and plan new transformations, etc.