Please note that the content of this book primarily consists of articles available from Wikipedia or other free sources online. UCLID is a decision procedure for CLU logic and can be used as a tool for bounded model checking of infinite-state systems. UCLID is a tool for verifying models of computer systems. It started out primarily focused on infinite-state systems, but now is equipped with techniques to also reason about word-level descriptions of systems. The key component of UCLID is a decision procedure for a decidable fragment of first-order logic, including uninterpreted functions and equality, integer linear arithmetic, finite-precision bit-vector arithmetic, and constrained lambda expressions.