The perfective aspect (abbreviated PFV), sometimes called the aoristic aspect, is a grammatical aspect that describes an action viewed as a simple whole, i.e., a unit without interior composition. The perfective aspect is distinguished from the imperfective aspect, which presents an event as having internal structure (such as ongoing, continuous, or habitual actions). The term perfective should be distinguished from perfect (see below).

The distinction between perfective and imperfective is more important in some languages than others. In Slavic languages, it is central to the verb system. In other languages such as German, the same form such as ich ging ("I went", "I was going") can be used perfectively or imperfectively without grammatical distinction. In other languages such as Latin, the distinction between perfective and imperfective is made only in the past tense (e.g., Latin veni "I came" vs. veniebam "I was coming", "I used to come"). However, perfective should not be confused with tense—perfective aspect can apply to events in the past, present, or future.

The perfective is often thought of as for events of short duration (e.g., "John killed the wasp"). However, this is not necessarily true—a perfective verb is equally right for a long-lasting event, provided that it is a complete whole; e.g., Tarquinius Superbus regnavit annos quinque et viginti (Livy) "Tarquin the Proud reigned for 25 years." It simply "presents an occurrence in summary, viewed as a whole from the outside, without regard for the internal make-up of the occurrence."

The perfective is also sometimes described as referring to a "completed" action, but it would be more accurate to say that it refers to an action or situation that is seen as a complete whole; e.g., the Russian perfective future я убью тебя "I shall kill you" refers to an event that has not yet been completed.

The essence of the perfective is an event seen as a whole. However, most languages that have a perfective use it for various similar semantic roles—such as momentary events and the onsets or completions of events, all of which are single points in time and thus have no internal structure. Other languages instead have separate momentane, inchoative, or cessative aspects for those roles, with or without a general perfective.

English has neither a simple perfective nor imperfective aspect; see imperfective for some basic English equivalents of this distinction.

When translating into English from a language that has these aspects, the translator sometimes uses separate English verbs. For example, in Spanish, the imperfective sabía can be translated "I knew" vs. the perfective supe "I found out", podía "I was able to" vs. pude "I succeeded", quería "I wanted to" vs. quise "I tried to", no quería "I did not want to" vs. no quise "I refused". The Polish perfective aspect is translated into English as a simple tense and the imperfective as a continuous; for example the imperfective oglądałem is translated into "I was watching", while the perfective obejrzałem is translated into "I watched". Such distinctions are often language-specific.

Languages may mark perfective aspect with morphology, syntactic construction, lexemes/particles, or other means.