Cardiovascular disease remains the leading cause of death in United States. Apolipoprotein A-I (apoA-I) is the major protein in high-density lipoprotein (HDL) and plays a vital role during the process of reverse cholesterol transport (RCT). Knowledge of the high-resolution structure of full-length apoA-I is essential for a molecular understanding of the function of HDL at various steps during the RCT pathway. Due to the flexible nature of apoA-I and inherent aggregation properties, the structure of full-length apoA-I has evaded description for over three decades. We use the techniques of modern molecular biophysics and structural biology to study the structure and function of apoA-I. We primarily rely on protein crystallography and molecular modeling coupled with SAXS to study the structure of apoA-I. In addition, circular dichroism, fluorescence microscope, electron microscopy, NMR and cellular assay are used to understand the function of apoA-I.