This book provides a semiotic analysis of computer programs along three axes: models of signs, kinds of signs, and systems of signs. Because computer programs are well defined and rigid, applying semiotic theories to them will help to reorganize the semiotic theories themselves. Moreover, semiotic discussion of programming theory can provide possible explanations for why programming has developed as it has and how computation is fundamentally related to human semiosis. The goal of this book is to consider the question of what computers can and cannot do, by analyzing how computer sign systems compare to those of humans. A key concept throughout is reflexivity - the capability of a system or function to reinterpret what it has produced by itself. Sign systems are reflexive by nature, and humans know how to make the most of this characteristic but have not yet fully implemented it into computer systems. Therefore, the limitations of current computers can be ascribed to insufficient reflexivity.