Some data types are so simple that they tend to be reimplemented over and over again. This is certainly true for terms, tree-like data structures that can represent prefix formulae, syntax trees, intermediate code, and more. We first describe the motivation to introduce Annotated Terms (ATerms): unifying several term formats, optimizing storage requirements by introducing maximal subterm sharing, and providing a language-neutral exchange format. Next, we present a brief overview of the ATerm technology itself and of its wide range of applications. A discussion of competing technologies and the future of ATerms concludes the paper.