An article of footwear is disclosed that includes an upper that defines an interior void, a sole structure secured to the upper, and a foot-supporting insert that is positionable within a lower area of the void and removable from the void. A system having a protrusion and an indentation may be utilized to, for example, secure the insert within the void. As an example, a protrusion may extend outward from a surface of the void, and the insert may define an indentation in a corresponding location and with a corresponding shape. When the insert is positioned within the void, the protrusion will extend into the indentation. The locations, shapes, numbers and overall configuration of the protrusion and indentation may vary significantly.