Drawing on the data and history from a wide range of languages, from Atayal to Zapotec, this volume brings together leading scholars in the field of tense and aspect research resulting in 18 contributions on the perfect and some of its close relatives (e.g. iamitives). Different approaches complement each other to shed light on the source, emergence, grammaticalization, and the typological extension of perfect constructions cross-linguistically. One focal point is the so-called aoristic drift, where the perfect comes to resemble the simple past or aorist (often via the hodiernal 'today' reading). The semantics and pragmatics of perfects are also investigated through their interaction with other categories (e.g. negation, mood). Over time some perfects undergo auxiliary doubling or omission, or the auxiliary becomes subject to selection. These facts also receive special attention in this book, presenting new insights on perfects in both well-studied as well as very understudied languages.