This page is a comprehensive tutorial on resistance, accompanied by three interactive simulations.  One allows the user to glimpse resistance at a molecular level; the second explores Ohm's Law; and the third introduces the use of color coding in composition resistors.  The author uses diagrams to illustrate arrangements of resistors in series and parallel circuits, with explanations of how to calculate equivalent resistances.  This item is part of a larger collection on Electricity and Magnetism sponsored by Florida State University.