This book offers a complete and systematic discussion on automatic recognition of printed and handwritten mathematical expressions. Efficiency of any optical character recognition (OCR) engine in recognizing scientific paper documents heavily depends on its ability to recognize mathematical expressions. Therefore, issues related to optical recognition of mathematical expressions are discussed in details. Online recognition of handwritten expressions is also covered as this provides a convenient alternative to keyboard or mouse used for preparing scientific documents on computer. The state of the art of the related research has been reviewed and then the recognition challenges have been discussed. Data sets and experimental procedures are outlined. Issues behind evaluating performance of an expression recognition system are also explained. The book has been concluded with a discussion on several aspects including development of common data sets and tools in order to facilitate further research on expression recognition.