Abdominal aortic aneurysm (AAA) is an increasingly common clinical condition with fatal implications. It is associated with advanced age, male gender, cigarette smoking, atherosclerosis, hypertension, and genetic predisposition. Although significant evidence has emerged in the last decade, the molecular mechanisms of AAA formation remain poorly understood. Currently, the treatment for AAA remains primarily surgical with the lone innovation of endovascular therapy. With advances in the human genome, understanding precisely which molecules and genes mediate AAA development and blocking their activity at the molecular level could lead to important new discoveries and therapies. This review summarizes recent updates in molecular mechanisms of AAA formation, including animal models, autoimmune components, infection, key molecules and cytokines, mechanical forces, genetics, and pharmacotherapy. This review will be helpful to those who want to recognize the newest endeavors within the field and identify possible lines of investigation in AAA.