Technical Abstract: Long-term plant breeding programs develop genetic resources that constitute the baseline potential of crop production systems. Over the course of time, through long-term plant breeding efforts, the volume of genetic resources developed is extensive. Knowledge of the performance and genetic properties of these genetic resources is critical to design efficient and effective plant breeding programs. As Upland cotton (Gossypium hirsutum L.) is a globally significant agricultural commodity, breeding and germplasm enhancement efforts have occurred for over 100 years. One of the most significant, long-term public cotton germplasm enhancement programs present in the US is known as the Pee Dee germplasm program. The unique, genetic foundation of the Pee Dee germplasm was created using germplasm from Upland, Sea Island, and primitive diploid cottons. Since the program’s inception in 1935, the Pee Dee germplasm program has developed and released over 80 improved germplasm lines and cultivars. In this study, we evaluated the agronomic and fiber quality performance of Pee Dee germplasm across southeastern US environments and estimated genetic improvement within the Pee Dee germplasm program over time. Results suggest that the unique foundation and breeding methods used in the Pee Dee germplasm enhancement program since 1935 have 1) maintained usable genetic diversity and 2) maintained high fiber quality potential while concomitantly improving agronomic performance. Although the results highlight the need to continue improving lint percent, lint yield, and bolls m-2, there is also evidence to suggest that Pee Dee germplasm can continue being utilized to develop the next generation of high fiber quality and high yielding cotton cultivars.