The improvement of process yields and efficiency are often dependent upon the availability of sensors that allow real-time in-process control. The sensitivity of impedance techniques to physical, chemical, and microstructural features of a material system offers significant potential in developing real-time sensors. Two examples of how impedance techniques can be used to follow changes in materials throughout out a process are discussed. The first of these involves monitoring the processibility and viability of solder pastes used in surface mount technology. The second example deals with monitoring the state of an ion exchange resin bed as used in water softeners.