The field of ergogenic aids and human physical performance has reached a point where conclusive experiments can be performed to answer basic questions. One can speculate, with a large degree of certainty, that psychological and training effects on performance are much greater than physiological effects of ergogenic aids. However, in cases where training, motivation, and talent are already optimized, ergogenic aids may provide a small but significant improvement in performance. Also, in practical settings, nutritional ergogenic aids provide a placebo effect not attainable otherwise. This chapter offers guidelines for use of those nutritional ergogenic aids for which available research has shown benefits for performance or for health conditions found in athletes, and illustrates the well-known advantages of water, electrolyte, and carbohydrate manipulations to maintain and enhance long-term endurance performance. As nutrients in general are given more credence for their biological attributes, nutritional ergogenic aids will become more sophisticated and effective.