Substituting infrared thermal sensors for conventional thermocouples to measure the temperature of a product, or a point in a process, often provides the industrial user with distinct advantages such as freedom from contact with the product and better speed of response. The major disadvantage has always been higher sensor cost. Now that costs of ir sensors have come down, the non-contact approach is becoming more of a valid alternative, and the instrument or process control engineer often weighs the relative advantages of the two approaches before making a decision. With the advent of "smart" thermal scanning systems, however, it is becoming possible to rapidly measure and control several, many or all points on a product surface remotely and without contact, a capability without precedent, and not feasible with conventional contact sensors. This paper will trace the evolution of infrared noncontact temperature measurement, its development as a process control tool and the introduction of IR line scanners and imagers as industrial control sensors. Several applications of modern closed-loop control systems based on infrared sensors, scanners and imagers will be reviewed. 1. INTRODUCTION Temperature and thermal behavior of materials and fabricated parts in process are most critical factors in the manufacturing process. For this reason temperature is by far the most measured quantity in industrial process monitoring and control. Conventional methods of temperature measurement using thermometers and thermocouples are commonly used for the majority of monitoring and control applications. Non-contact temperature measurement using infrared sensors has become an increasingly desirable alternative over conventional methods as ir sensors have become less expensive, more reliable and electrically interchangeable with conventional thermistors and thermocouples. Now, with the introduction of innovative computer hardware and software, full image thermal control of products and processes is being made possible.