Modern process control requires current information on the state (composition, temperature, pressure, flow rate, etc.) of the material being produced. Modern distributed control systems linked to various control elements (valves, pumps, etc.) require data much more often than the manual control systems of years gone by. While grab samples taken to a modern laboratory will be the gold standard for quality control purposes, the effort and time it takes to get a sample, transport it to the lab, and wait for the result can add significantly to the costs of the process in process output, energy, etc. For many industries, the solution is to move the analysis directly to the process. This need for more and better analyzers does not mean that their application is, or ever will be, a simple, routine task. For an analyzer system to fulfill its expectations, careful planning and evaluation must precede its purchase, and the users must realize that if an expensive analyzer is worth purchasing, it must also be worth calibrating and maintaining. The operator’s acceptance, which depends largely on training and familiarization, is also crucial. New self-diagnosing and self-calibrating analyzers are a major contribution to improved operator acceptance, but people issues are still more important and should not be discounted.Defining the problem begins with understanding how the measurement will be used. Is it for closed-loop process control or for information purposes? Is the measurement really needed “on-line,” or could 80% of the benefits be obtained for 20% of the cost and effort by making the measurement “at-line” in the control room? What is the benefit of the measurement? How will the cost be justified? Is this to reduce staffing by moving the measurement from the lab to the pipe? Is it a yield-improvement project? Answers to these questions begin to clarify the needed timescale for the measurement. In addition, it is important to understand the process to be monitored. What is the response time of the process? Obviously, if the process takes 60 min to respond to a temperature change (e.g., distillation column), analyzer requirements are quite different from those of a process that responds in 6 sec.