Use the Splitter.Dock property to define how a control is automatically resized as its parent control is resized. You can only set the Splitter.Dock property to DockStyle.Top, DockStyle.Bottom, DockStyle.Left, or DockStyle.Right. The System.Windows.Forms.Splitter control enables the user to resize the docked control that is immediately before it in the docking order. Therefore, to enable the user to resize a docked control, dock the control to an edge of a container, and then dock a System.Windows.Forms.Splitter control to the same side of that container. For more information, see the example in the System.Windows.Forms.Splitter class.