The paper introduces a new user interface called the see-through interface, which uses Toolglass widgets and Magic Lens filters. These tools appear on a virtual transparent sheet between the application and a traditional cursor, allowing users to interact with application objects in a new way. Toolglass widgets can be positioned with one hand while the other controls the cursor, and they can incorporate Magic Lens filters that modify the presentation of application objects to reveal hidden information, enhance data of interest, or suppress distracting information. The see-through interface offers advantages over traditional controls by providing a new style of interaction that better exploits the user's everyday skills, reduces steps, cursor motion, and errors, and allows for rich context-dependent feedback and simultaneous viewing of details and context. The interface can be used in various application domains and allows for the creation of operation and viewing macros across multiple applications. The see-through interface is implemented in the Multi-Device Multi-User Multi-Editor (MMM) framework in the Cedar programming language, running on SunOS UNIX on Sun Microsystems SPARCstations. The Gargoyle graphics editor is used as a complex application to test the interface. The interface uses a standard mouse for the dominant hand and a MicroSpeed FastTRAP trackball for the non-dominant hand. The trackball includes three buttons and a thumbwheel, which can be used to supply additional parameters to the interface. The paper discusses related work in four areas: multi-handed interfaces, movable tools, transparent tools, and viewing filters. It describes examples of tools developed, including shape and property palettes, clipboards, previewing lenses, and selection tools. The see-through interface allows for the creation of customized libraries of shapes and properties and provides a new paradigm for computer graphics artists and scientific visualization. The interface is also useful for reducing task steps and learning time, providing good graphical feedback, and allowing users to construct their own control panels and spatial modes. Future work includes exploring the current space of possibilities, creating new widgets in different application domains, and designing new conventions for composing, editing, navigating, organizing, and triggering these tools.The paper introduces a new user interface called the see-through interface, which uses Toolglass widgets and Magic Lens filters. These tools appear on a virtual transparent sheet between the application and a traditional cursor, allowing users to interact with application objects in a new way. Toolglass widgets can be positioned with one hand while the other controls the cursor, and they can incorporate Magic Lens filters that modify the presentation of application objects to reveal hidden information, enhance data of interest, or suppress distracting information. The see-through interface offers advantages over traditional controls by providing a new style of interaction that better exploits the user's everyday skills, reduces steps, cursor motion, and errors, and allows for rich context-dependent feedback and simultaneous viewing of details and context. The interface can be used in various application domains and allows for the creation of operation and viewing macros across multiple applications. The see-through interface is implemented in the Multi-Device Multi-User Multi-Editor (MMM) framework in the Cedar programming language, running on SunOS UNIX on Sun Microsystems SPARCstations. The Gargoyle graphics editor is used as a complex application to test the interface. The interface uses a standard mouse for the dominant hand and a MicroSpeed FastTRAP trackball for the non-dominant hand. The trackball includes three buttons and a thumbwheel, which can be used to supply additional parameters to the interface. The paper discusses related work in four areas: multi-handed interfaces, movable tools, transparent tools, and viewing filters. It describes examples of tools developed, including shape and property palettes, clipboards, previewing lenses, and selection tools. The see-through interface allows for the creation of customized libraries of shapes and properties and provides a new paradigm for computer graphics artists and scientific visualization. The interface is also useful for reducing task steps and learning time, providing good graphical feedback, and allowing users to construct their own control panels and spatial modes. Future work includes exploring the current space of possibilities, creating new widgets in different application domains, and designing new conventions for composing, editing, navigating, organizing, and triggering these tools.