Examining the layers of meaning encoded in software and the rhetoric surrounding it, this book offers a much-needed perspective on the intersections between software, morality, and politics. In software development culture, evangelism typically denotes a rhetorical practice that aims to convert software developers, as well as non-technical lay users, from one platform to another (e.g., from the operating system Microsoft Windows to Linux). This book argues that software evangelism, like its religious counterpart, must also be understood as constructing moral and political values that extend well beyond the boundaries of the development culture. Unlike previous studies that locate such values in the effects of code in-use or in certain types of code like free and open source (FOSS) software, Maher argues that all code is meaningful beyond its technical, executable functions. To facilitate this analysis, this study builds a theory of evangelism and illustrates this theory at work in the proprietary software industry and FOSS communities. As an example of political liberalism at work at the level of code, these evangelical rhetorics of software construct competing conceptions of what is good that fall within a shared belief in what is just. Maher illustrates how these beliefs in goodness and justice do not always execute in replicable ways, as the different ways of decoding software evangelisms in the contexts of Brazil and China reveal. Demonstrating how software evangelisms exert a transformative force on the world, one comparable in significance to code itself, this book highlights the importance of rhetoric in even the most seemingly a-rhetorical of technical endeavors and foregrounds the crucial need for rhetorical literacy in the digital age.