Technical Abstract: Moisture is an important quality, processing, and marketing parameter for cotton fiber. The accurate and precise measurement of fiber moisture continues to be an issue of importance in the global marketplace. There are several commercially available moisture measurement instruments for fiber moisture measurements in the laboratory, at-line, and the bale (at-line and on-line). These moisture units typically use the ASTM oven method (thermal gravimetric) as the reference method for moisture. Several at-line and bale (at-line and on-line) moisture measurement systems are reviewed, and their technical capabilities discussed. Most often, it is desired for these at-line and on-line systems to agree closely with laboratory fiber moisture measurements. There are several forms and types of laboratory fiber moisture measurements and measurement systems, each with their own advantages and disadvantages. Moisture measurements and systems can generally be divided into thermal, chemical, spectroscopy, and “electric” categories. Several of the more common fiber moisture measurement systems were compared on a set of domestic and international cottons, using the oven method as the reference method. Most of the fiber moisture measurements and systems yielded acceptable/good agreement to the oven method (within ±0.5% moisture with the oven method for greater than 90% of the samples analyzed). However, few of these systems agreed to the much tighter—and desired—method agreement of within ±0.3% moisture for greater than 80% of the samples analyzed. A comprehensive Comparison Matrix was developed that combines both non-technical and technical attributes so as to assist the potential purchaser in selecting the best overall moisture measurement system for their needs. The commercial moisture units typically use the ASTM oven method (thermal gravimetric) as the reference method for moisture. New research is focusing on a chemical method as the reference method for fiber moisture, and the status of this research is reviewed. In general, the chemical method yields lower moisture compared to the oven method.