Evernote supports unicode subscript and superscript characters. Naturally you're limited by the available unicode subscript and superscript characters (see http://en.wikipedia.org/wiki/Wikipedia:Unicode_subscripts_and_superscripts ). Not every character is available as a sub- or superscript, but many are. I'm a mac user, and fortunately Evernote supports OSX-wide text substitution. Go to System Prefs > Language & Text > Text and create text substituions such as _2 on the left and ₂ on the right. Now when you type CO_2 in Evernote, it automatically changes to CO₂. You can also set, for example, <inf> to be substituted to ∞, or any string to any unicode character or string of other unicode characters. For a complete list of available characters, go to Edit > Special Characters in just about any mac app. I imagine a similar solution must exist for users of other OSes. Obviously, this is not a 100% solution, but it's good enough in most cases. I use a LaTeXiT service when this isn't enough.