Men who have sex with men (MSM) are disproportionately impacted by syphilis. In 2019, 56.7% of all primary and secondary (P&S) syphilis infections among men were among MSM. Rates of P&S syphilis have increased more rapidly among MSM than any other subpopulation, from 20.6 per 100,000 in 2000 to 272.8 per 100,000 in 2015. Untreated syphilis can lead to severe medical complications, including infertility, pregnancy loss, and severe neurological and ocular complications. However, little is known about how temporal changes in sexual network structures among MSM may influence syphilis epidemiology, promote racial/ethnic disparities, and hinder efforts to control syphilis with traditional network-informed interventions, including contact tracing. This project aims to bridge gaps in current knowledge and understanding of syphilis epidemiology among MSM using a prospective longitudinal cohort study called the Network Epidemiology of Syphilis Transmission Study (NEST) to model the individual-level and network-level factors contributing to epidemic syphilis among MSM in the US.