'Language attrition' describes the loss of, or changes to, grammatical and other features of a language as a result of declining use by speakers who have changed their linguistic environment and language habits. In such a situation there may, for example, be simplification in the tense system or in certain properties of subordinate clauses; some vocabulary items might fall into disuse and phonetic features may be restructured. These changes can be affected by features of the speaker's environment, but also by his or her attitudes and processes of identification. This book provides a detailed and up-to-date introduction to the way in which language attrition can affect language, as well as to the extra- and sociolinguistic features involved. It also familiarizes the reader with experimental approaches to attrition and data analysis techniques and provides hands-on guidelines on how to apply them.