This paper discusses the application of MWD tools in various types of drilling operations to enhance drilling safety and efficiency. The resistivity tools from various MWD suppliers in the U.S. have been used for various applications. MWD tools can be effectively used to detect abnormal pressure zones, to select coring points, to optimize bit loading, to predict bit wear, to identify faults, and to detect influxes.There are three main types of MWD resistivity tools. Special features and limitations of each tool are presented.