In the realm of FPGAs, many tool vendors offer behaviorally-based simulators aimed at easing the complexity of large FPGA designs. At times, a behaviorally-modeled design does not work in hardware as expected or intended. VTsim, a Virtex-II device simulator, was designed to resolve this and many other design problems by providing a window into the FPGA fabric via a virtual device. VTsim is an event-driven device simulator modeled at the CLB level with multiple clock domain support. Utilizing JBits3 and ADB, VTsim enables simulation and examination of all resources within an FPGA via a virtual device. The only input required by VTsim is a bitstream, which can be generated from any tool suite. The simulator is part of the JHDLBits open-source project, and was designed for rapid response, low memory usage, and ease of interaction. / Master of Science