Gossypium barbadense L. (Egyptian and Pima) produces single-celled fiber trichomes that are the longest and richest in cellulosic content in the plant kingdom. Developmental dissection of fiber at the transcriptional level is crucial to unveil the genetic mechanisms underpinning fiber morphogenesis. This book describes the transcriptome of developing cotton fibers, as well as genes associated with consensus fiber quality QTL, at seven developmental time points covering both primary (PCW) and secondary (SCW) cell wall stages. By integrating stage-specific gene profiles, fiber developmental stages, and developmentally regulated quantitative trait loci (drQTL), I proposed a developmental model connecting gene expression profiles and fiber traits. The model identifies the major genes and metabolic process underpinning the main fiber quality traits.