Producers, consultants and researchers have long sought a quick, reliable method to diagnose cotton N status during the growing season. Soil and plant N testing have provided a means to estimate cotton N needs, but these methods are sometimes time consuming and can be costly. The development of a hand-held chlorophyll meter, which can be used to estimate crop N, has generated much interest in use of this tool for developing mid-season cotton N recommendations. The theory behind chlorophyll meter technology is discussed in this proceedings.