Technical Abstract: An 18-environment field study was undertaken to observe lint yield stability in four population types of cotton (Gossypium hirsutum L.) that included: pure lines grown in pure stands (homozygous/homogeneous), pure lines grown in blended stands (homozygous/ heterogeneous), hybrids grown in pure stands (heterozygous/homogeneous), and hybrids grown in blended stands (heterozygous/heterogeneous). Cotton lint yield was measured on each plot. Population types were compared using trait means, standard deviation (SD), and the coefficients of variation (CV) calculated over environments. The heterozygous populations had a higher mean yield than the homozygous populations; this difference was attributed to heterosis but was not consistent over environments and diminished as environmental mean increased (correlation of -0.72). The heterozygous populations had a lower CV (were more stable) than the homozygous populations. This stability was attributed to the heterozygous populations having a reduced range in yields as compared to the homozygous populations, such that the hybrids and blends of hybrids out-yielded the parents and blends of parents in the low-yielding environments but had similar yields in the high-yielding environments.