Borrowing money to purchase securities is known as "buying on margin." The concept may sound simple, however understanding it can be anything but. To help our customers grasp the implications and requirements of trading on margin, we have redesigned our series of margin information pages which discuss everything from the concepts of initial and maintenance margin to the specific calculations for determining margin at the time of trade. Graphical examples make this complex topic easier to understand. Get started by clicking marginon the Trading menu.