Cresus is a unique application of state-of-the-art expert system technology to the real-world financial problem of cash management. By automating the work of company treasurers, it saves substantial amounts of both money and time every day. Real-world test cases show that cresus performs better and much faster than the human expert: In minutes, it generates a combination of operations that efficiently balances all banking accounts in a 15-day period. It uses user-friendly window technology to control the human-machine dialogue and has been integrated into the work environment of a major electric company in Spain. Written in Common Lisp using unix workstations, it was jointly developed by Union Fenosa, Carnegie Mellon University, and Norsistemas Consultores.