The lack of a common, structured vocabulary to describe cotton phenotypic traits is an obstacle for researchers wanting to understand the work of colleagues as well as for integration of QTL associated with these traits into CottonGen. Cotton Trait Ontology (a set of standardized and structured vocabularies for cotton traits) aims to provide a central location with controlled vocabulary for phenotypic traits to improve discussion and collaboration among research groups within the cotton community. The terms in the Cotton Trait Ontology were developed from trait evaluation data within five germplasm collections from four countries and from QTL-trait association data obtained from over one hundred peer-reviewed publications. The vocabulary was established by CottonGen with input from Drs. Lori Hinze, Richard Percy, and Russell Kohel (USDA-ARS, College Station, TX).