This chapter contains 12 well illustrated diagrams. Chapter has description of intra operative monitoring of functions of different parts of nervous system. A detailed description is given from selection of machine for intra operative monitoring to choosing software of the same. A table is added to summarise features to be monitored intra operatively. It covers comprehensively intra operative electromyography, electrocorticography. Intraoperative magnetic resonance imaging and cerebral blood flow monitoring by laser speckle contrast analysis are dealt with great detail. 47 references are given for further reading at the end of the chapter.