Protein structures are hard to represent on paper. They are large, complex, and three-dimensional (3D)--four-dimensional if conformational changes count! Unlike most of their substrates, which can easily be drawn out in full chemical formula, drawing every atom in a protein would usually be a mess. Simplifications like showing only the surface of the protein or showing only a trace between its alpha carbons are preferred methods for representing the overall structure of a protein, and zoomed-in views showing all of the atoms in a certain part of the protein can highlight important residues. Unfortunately, even these simplifications can look confusing when flattened into two-dimensional images as in printed textbooks and scientific publications. This article introduces "Proteopedia" (http:/www.proteopedia.org), a new collaborative web resource with pages describing protein, nucleic acid, and other biomolecule structures--including complexes--in interactive, virtual 3D. Educators have found "Proteopedia" to be a useful teaching tool, and several instructors have adopted "Proteopedia" into their classrooms. The most obvious use is viewing existing user-added pages on molecules of interest.