GridBagLayout respects the preferred size of the components it is given to layout. It asks each component for the size it requires for proper display. In turn the component will get this information from its layout manager which asks the child components of the component (lots of components in here). If the component has no children then it will report a default size such as (0,0) or (10,10). You can specify size hints for your JPanels with the setPreferredSize method (which is also a Component (AWT) method in j2se 1.5). The gridbag layout manager can use this to display your panels. A trick you can use is to add an etched border or background color to your panels to track them as you build up your gui. You can also control the display size of components with combinations of the weight and fill constraints but this is more advanced.