A friend asked us once, “Should I use LaTeX or MiKTeX?” In various guises, this is a common question, seemingly innocent, but actually betraying a fundamental confusion about the levels of operation in the TeX world. As a further confusion, the word “TeX” can be used to refer to any of a myriad of items at any level. Starting at the top: Distributions: MiKTeX , TeX Live , … These are the large collections of TeX-related software to be downloaded and installed. When someone says “I need to install TeX on my machine”, they're usually looking for a distribution. Front ends: Emacs , TeXworks , TeXShop , TeXnicCenter , WinEdt , … These editors are what you use to create a document file. Some (e.g., TeXShop) are devoted specifically to TeX, others (e.g., Emacs) can be used to edit any sort of file. TeX documents are independent of any particular editor; the TeX typesetting program itself does not include any sort of editor whatsoever. Engines: TeX, pdfTeX , XeTeX , LuaT...