Measuring operator fatigue is an important component of fatigue management in transport. To do it in a meaningful and reliable manner, it is essential before actual measurements to (a) define the main purpose of the measurements, (b) identify the target group and setting, and (c) make a plan for utilisation of the measured data. These steps will help one choose the right method(s) for the job. Generally, it is recommended to choose more than one method, for none of the methods available capture all manifestations of fatigue. When measuring operator fatigue in field settings, it is a good idea to have more than one measurement point per duty period and a well-rested reference condition (e.g., day trip) against to which compare the potentially fatiguing condition (e.g., night trip). Finally, sufficient knowledge of the strengths and weaknesses of fatigue measurement methods makes is possible to interpret the results obtained in a correct way and thus draw reliable conclusions from measurements.