In general, there have been two principal approaches to the assessment of physical performance (1) field tests of physical fitness and performance, which include a variety of measurements requiring basic performance demands, and (2) laboratory assessments of physiological capacities such as maximal aerobic power (V02 max), anaerobic power, and exercise economy. it can be argued that physical fitness testing is important for an overall assessment of general conditioning, particularly in terms of evaluating Student progress in a conditioning class (1, 68). However, the use of these test batteries does not provide the detailed physiological information needed to assess an athlete’s level of conditioning or potential weaknesses. Therefore, more specific laboratory tests are required to provide detailed physiological information about performance in specific athletic events. This chapter will discuss tesrs designed to measure physical work capacity and performance in athletes. Specifically, much of this chapter will focus on both laboratory and field tests to evaluate the maximum energy transfer capacities discussed in Chaps. 3 and 4. The performance tests described in this chapter differ from the exercise tests described in Chap. 15 in several ways. Recall that the exercise tests described in Chap. 15 were targeted toward assessing cardiorespiratory fitness in healthy adults entering or actively engaged in a regular ‘health-related' exercise program. in contrast, the exercise tests described in this chapter are targeted toward measurement of performance in athletes actively engaged in competitive sports. Let’s begin with a discussion of the theory and ethics of laboratory assessment of performance.