Adolescents and emerging adults face disproportionately high rates of adverse sexual health outcomes, including sexually transmitted diseases (STDs) and human immunodeficiency virus (HIV), unintended pregnancies, and sexual violence victimization (SVV). These risks are often linked to the developmental stage in which youth explore romantic and sexual relationships. Effective sexual health communication (SHC) is a known protective factor that promotes healthier sexual practices. Despite its empirical protective function, SHC remains poorly defined and inadequately measured, limiting our understanding of its full impact. Existing research suggests that discussing sexual health with partners can be protective, yet the mechanisms through which SHC influences outcomes remain unclear. Furthermore, SHC has the potential to be ineffective, inaccurate, or inappropriate, thus having a detrimental impact. This dissertation aims to better define and measure SHC to adequately explore its influence in practice. The dissertation consists of three interrelated studies that collectively explore how SHC mitigates risk behaviors and associated adverse outcomes. The first study employs qualitative methods to conceptualize SHC practices among emerging adults, identifying influences of sex education sources and extrapolating how these sources contribute to their SHC experiences. Building on these findings, the second study develops a novel comprehensive, multidimensional measure of SHC, informed by both the qualitative data and existing literature, using a large sample of young adults. The third study validates this new measure and examines the associations between SHC and factors that shape communication, such as sexual health knowledge, sexual pleasure communication, and experiences of victimization. Findings reveal that SHC among emerging adults is complex and affected by intra- and interpersonal elements. The newly developed measure captures the multifaceted nature of SHC and identifies key determinants that either facilitate or hinder sexual health discussions. By deepening the understanding of SHC, this research offers critical insights to inform intervention design aimed at promoting healthier sexual behaviors and improving sexual health outcomes.