Computer scientists, mathematicians, and physicists are collaborating with cell biologists to build a tool, "Virtual Cell", that can merge data of cellular biochemistry with knowledge of cell structure to help us understand how cells produce complex behaviors. A cell is a highly complex factory that organizes thousands of different molecules to produce a specialized function. Microscopists have catalogued a wealth of data about the detailed structures within different types of cells and biochemists have assembled details about the properties and reactions of many of a cell's individual molecular constituents. The experimental information gathered from the test tube and from the microscope is married within "Virtual Cell" to construct a computer model which can produce simulations of how cells carry out a given function (e.g. secretion of insulin, contraction of heart muscle). What is produced are digital movies showing how each molecular species moves and reacts inside the cell during the cell biological process. Perhaps the most exciting application of this tool is that it allows scientists to ask questions about what happens when one step in a complex chain of events misfires or how a drug that is known to affect just a single enzyme might change the way a cell carries out a specific function. But in addition to its use as a research tool, "Virtual Cell" can be a valuable teaching aid and may serve as a focus for organizing the tremendous knowledge base that comprises modern cell biology and biochemistry.The Virtual Cell is a fully modular computational framework that permits construction of models, application of numerical solvers to perform simulations, and analysis of simulation results. An intuitive JAVA interface includes options for database access, geometry definition (including directly from experimental images), specification of compartment topology, species definition and assignment, chemical reaction input, and computational mesh. Deterministic and stochastic physical formulations have been implemented. The algorithms have been rigorously tested against exact solutions including various membrane and boundary conditions. This talk will describe the status of the project and provide a demonstration of several applications to cell biological problems.