This paper argues that indexation markers (i.e., argument-indexing agreement markers and/or pronouns) show a wider range of formal mismatches across languages than the exponents of other inflectional categories. These mismatches are defined in terms of mixed behavior with respect to different criteria of wordhood. The mismatches that the indexation markers (or “indexes”) show include extrametricality with respect to reduplication and “mobility” in that they can occur in different slots of otherwise identical word forms. Other indexes can freely occur on either member of a phrase-level construction or behave like full-fledged affixes in one context but like full-fledged words in another. The claim that the range of these traits is extraordinary is based on a larger project, (Zingler, Tim. 2020. Wordhood issues: Typology and grammaticalization. Albuquerque: University of New Mexico PhD dissertation), which in addition to indexes investigates mismatches among case, definiteness, and tense markers. The explanations offered for this behavior primarily rely on the manner in which reference is established in discourse and on the different diachronic pathways for which these usage patterns pave the way. Another major conclusion is that the indexes described here constitute a formally heterogeneous set that cannot be easily subsumed under the label of “clitics.”