The field of software is awash in disputes. Market participants and analysts routinely disagree on how computer programs should be produced, marketed, regulated, and sold. On one subject, however, just about everyone can agree: the current intellectual property protection regime for software is a mess. At present, all of the traditional means of delimiting intellectual property — patents, copyrights, and trade secrets — are applied to software in one manner or another. Congress has even invented a new type of law for cases in which these may be insufficient, with the Digital Millennium Copyright Act. The result is widespread confusion, along with the proliferation of nuisance suits. To date, the U.S. Patent and Trademark Office has granted more than 170,000 software patents, some on applications as commonplace as the pop-up window. Each of these patents gives the holder the right to sue others where no such right existed before, and so gaming of the system abounds. Software providers are forced to funnel millions of dollars annually into defending themselves against lawsuits rather than developing better software. The wave of litigation may end up stifling innovation and hobbling the open source movement, one of the most promising developments of recent years. How did the situation arise? And where should we go from here? In Math You Can’t Use, Ben Klemens draws on his experience as both a programmer and an economist to tackle these critical issues. The answer to the first question, he explains, is simple: while patent laws are intended to apply to physical machines, software is something quite different. Software is not just another machine, and it is not Hamlet with numbers. It is a functional hybrid that can be duplicated at no cost, it is legible by computers in some forms and by humans in others, and it has a unique mathematical structure. All of these facts have to be taken into consideration in designing an appropriate intellectual property regime. Designing such a system is a more difficult task. Klemens considers several alternatives, from modifying the existing rules to eliminating software patents in favor of a copyright-centered regime. Ultimately, he concludes, it is up to Congress to determine how software should be protected.