Like nearly all retroviruses, HIV-1 selectively packages two copies of its full-length genome after the formation of a dimer – a process essential not only to packaging but also reverse transcription and recombination. The dimerization process has been found to be mediated by the untranslated region of the HIV-1 transcript, the 5′-Leader, a nearly 400 nucleotide region of the RNA genome that is found to be responsible for regulating RNA fate and function. Structural methods on large RNAs like the dimeric leader (~800 nts) are notoriously limited due to the their inherent flexibility and size; however, more recent methodologies within the Summers lab have allowed us to characterize secondary structure domains within the intact leader. Using these defined structures, we can analyze how different domains of the leader influence RNA function and affect the viral life cycle. The goal of this thesis is to characterize the HIV-1 genomic dimer. We specifically looked at different domains and how they regulate dimerization and subsequent functional processes. We were specifically able to study the function of the 5′-polyadenylation signal, protein coding sequence downstream of the leader, the dimerization initiation site, and the major splice donor. We aimed to characterize processes such as dimerization, packaging, and even translation. Our work also sought to answer a long-standing question about the HIV-1 retroviral lifecycle: how could a single RNA transcript produce protein and also serve as the viral genome? We believe the process relies on the production of two different transcripts with different start sites, which modulate dimerization, but more importantly the structure at the 5′-cap which seems to subsequently dictate RNA fate. Overall, this work highlights the dynamic nature of RNA processes and how small changes in sequence can lead to dramatic changes in the HIV-1 lifecycle. We show that the role of dimerization within the HIV lifecycle is misunderstood, and still requires further characterization to understand how this structure dictates all its necessary functions. Our hope is that understanding the RNA processes involved in HIV-1 replication will allow the development of new therapeutic targets for treatment of the still ongoing HIV epidemic.