Written communication in instant messaging, text messaging, chat, and other forms of electronic communication appears to have generated a "new language" of abbreviations, acronyms, word combinations, and punctuation. In this naturalistic study, adolescents collected their instant messaging conversations for a 1-week period and then completed a spelling test delivered over instant messaging. We used the conversations to develop a taxonomy of new language use in instant messaging. Short-cuts, including abbreviations, acronyms, and unique spellings were most prevalent in the instant message conversation, followed by pragmatic signals, such use of emoticons, emotion words, and punctuation, and typographical and spelling errors were relatively uncommon. With rare exceptions, notably true spelling errors, spelling ability was not related to use of new language in instant messaging. The taxonomy provides an important tool for investigating new language use and the results provide partial evidence that new language does not have a harmful effect on conventional written language.