Endovascular repair of abdominal aortic aneurysms shows promising initial results. Endoleaks represent one of the unique causes of endovascular repair failure not seen with traditional abdominal aortic aneurysm repair. Endoleaks occur when there is blood flow outside the stent-graft lumen but within the aneurysm sac. They can be difficult to diagnose and treat, and their management is a source of continued controversy. This review further defines endoleaks and the clinical challenges that they create. Current methods for endoleak detection, classification, and management are reviewed.