Planning is one of the most important, yet often one of the most poorly executed, steps in chemical measurements. Sometimes this is due to expediency. Planning involves several aspects of the analytical system. Selection of relevant samples and appropriate methodology is obviously involved. The development of the measurement plan may be based on statistical design or on professional judgment. In complex programs, the former is often necessary. The measurement plan describes the checkout plan to verify statistical control, prior to measurement, and the measurement schedule to be followed. The sequence of samples, controls, blanks, and calibrations should be planned and stated. The details of calibration should be described. This includes the materials to be used, how standards are to be prepared, and how the confidence in them is to be established and quantified. The controls to be used must be described together with the frequency of their use.