The past tense is a grammatical tense whose principal function is to place an action or situation in past time. In languages which have a past tense, it thus provides a grammatical means of indicating that the event being referred to took place in the past. Examples of verbs in the past tense include the English verbs sang, went and was.

In some languages, the grammatical expression of past tense is combined with the expression of other categories such as mood and aspect (see tense–aspect–mood). 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, an imperfect for expressing events which were ongoing or repeated in the past, as well as several other past forms.

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.

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