On displays with high pixel densities or on mobile devices and due to limitations in current graphical user interface toolkits, content can appear (too) small and be hard to interact with. We present WidgetLens, a novel adaptive widget magnification system, which improves access to and interaction with graphical user interfaces. It is designed for usage of unmodified applications on screens with high pixel densities, remote desktop scenarios, and may also address some situations with visual impairments. It includes a comprehensive set of adaptive magnification lenses for standard widgets, each adjusted to the properties of that type of widget. These lenses enable full interaction with content that appears too small. We also present several extensions.