The past tense is a grammatical tense whose function is to place an action or situation in the past. Examples of verbs in the past tense include the English verbs sang, went and washed. Most languages have a past tense, with some having several types in order to indicate how far back the action took place. Some languages have a compound past tense which uses auxiliary verbs as well as an imperfect tense which expresses continuous or repetitive events or actions. Some languages inflect the verb, which changes the ending to indicate the past tense, while non-inflected languages may use other words meaning, for example, "yesterday" or "last week" to indicate that something took place in the past.

In some languages, the grammatical expression of past tense is combined with the expression of other categories such as grammatical aspect (see tense–aspect). Thus a language may have several types of past tense form, their use depending on what aspectual or other additional information is to be encoded. French, for example, has a compound past (passé composé) for expressing completed events, and imperfect for continuous or repetitive events.

Some languages that grammaticalise for past tense do so by inflecting the verb, while others do so periphrastically using auxiliary verbs, also known as "verbal operators" (and some do both, as in the example of French given above). Not all languages grammaticalise verbs for past tense – Mandarin Chinese, for example, mainly uses lexical means (words like "yesterday" or "last week") to indicate that something took place in the past, although use can also be made of the tense/aspect markers le and guo.

The "past time" to which the past tense refers generally means the past relative to the moment of speaking, although in contexts where relative tense is employed (as in some instances of indirect speech) it may mean the past relative to some other time being under discussion. A language's past tense may also have other uses besides referring to past time; for example, in English and certain other languages, the past tense is sometimes used in referring to hypothetical situations, such as in condition clauses like If you loved me ..., where the past tense loved is used even though there may be no connection with past time.

Some languages grammatically distinguish the recent past from remote past with separate tenses. There may be more than two distinctions.

In some languages, certain past tenses can carry an implication that the result of the action in question no longer holds. For example, in the Bantu language Chichewa, use of the remote past tense ánáamwalíra "he died" would be surprising since it would imply that the person was no longer dead. This kind of past tense is known as discontinuous past. Similarly certain imperfective past tenses (such as the English "used to") can carry an implication that the action referred to no longer takes place.

A general past tense can be indicated with the glossing abbreviation PST.

The European continent is heavily dominated by Indo-European languages, all of which have a past tense. In some cases the tense is formed inflectionally as in English see/saw or walks/walked and as in the French imperfect form, and sometimes it is formed periphrastically, as in the French passé composé form. Further, all of the non-Indo-European languages in Europe, such as Basque, Hungarian, and Finnish, also have a past tense.