VirtualMicroscope is a Python/Django application to view, navigate and annotate very high-resolution images. It was created at New York University School of Medicine for viewing medical slides for teaching and research purposes, where it has proved very successful, but in the basic principle is suitable for exploring any high-resolution images - from astronomy, museum collections, specialised photographic applications and so on. The application makes use of image tiling (and specifically, Google Maps's implementation of this, though other tiling systems could be used) to make it possible to view and zoom into images tens or even hundreds of GB in size. In medicine and science, a virtual microscope relieves pressure on laboratories and equipment, and makes it possible to to collaborate remotely - without needing to transport precious slides or colleagues. More generally, the technology simply makes it possible to view huge images.