 The purpose of this entry is to explore how atheism and agnosticism are related to theism and, more importantly, to each other. This requires examining the surprisingly contentious issue of how best to define the terms “atheism” and “agnosticism”. Settling this issue, at least for the purposes of this entry, will set the stage for discussing an important distinction between global atheism and local atheism, which in turn will be helpful for distinguishing different forms of agnosticism. Examination of an argument in support of a modest form of agnosticism will ensue, followed by discussion of three arguments for atheism and one argument against a more ambitious form of agnosticism.