In linguistics, word order (also known as linear order) is the order of the syntactic constituents of a language. Word order typology studies it from a cross-linguistic perspective, and examines how different languages employ different orders. Correlations between orders found in different syntactic sub-domains are also of interest. The primary word orders that are of interest are

• the constituent order of a clause, namely the relative order of subject, object, and verb;
• the order of modifiers (adjectives, numerals, demonstratives, possessives, and adjuncts) in a noun phrase;
• the order of adverbials.

Some languages use relatively fixed word order, often relying on the order of constituents to convey grammatical information. Other languages—often those that convey grammatical information through inflection—allow more flexible word order, which can be used to encode pragmatic information, such as topicalisation or focus. However, even languages with flexible word order have a preferred or basic word order,with other word orders considered marked.

These are all possible word orders for the subject, object, and verb in the order of most common to rarest (the examples use she as the subject, loves as the verb, and him as the object):

• SOV is the order used by the largest number of distinct languages; languages using it include Japanese, Korean, Mongolian, Turkish, the Indo-Aryan languages and the Dravidian languages. Some, like Persian, Latin and Quechua, have SOV normal word order but conform less to the general tendencies of other such languages. A sentence glossing as She him loves would be grammatically correct in these languages.
• SVO languages include English, Bulgarian, Macedonian, Serbo-Croatian, the Chinese languages and Swahili, among others. She loves him.
• VSO languages include Classical Arabic, Biblical Hebrew, the Insular Celtic languages, and Hawaiian. Loves she him.
• VOS languages include Fijian and Malagasy. Loves him she.
• OVS languages include Hixkaryana. Him loves she.
• OSV languages include Xavante and Warao. Him she loves.

In many languages, standard word order can be subverted in order to form questions or as a means of emphasis. In languages such as O'odham and Hungarian, which are discussed below, almost all possible permutations of a sentence are grammatical, but not all of them are used.[15] In languages such as English and German, word order is used as a means of turning declarative into interrogative sentences:

• A: 'Wen liebt Kate?' / 'Kate liebt wen?' [Whom does Kate love? / Kate loves whom?] (OVS/SVO)
• B: 'Sie liebt Mark' / 'Mark ist der, den sie liebt' [She loves Mark / It is Mark whom she loves.] (SVO/OSV)
• C: 'Liebt Kate Mark?' [Does Kate love Mark?] (VSO)

In (A), the first sentence shows the word order used for wh-questions in English and German. The second sentence is an echo question; it would only be uttered after receiving an unsatisfactory or confusing answer to a question. One could replace the word wen [whom] (which indicates that this sentence is a question) with an identifier such as Mark: 'Kate liebt Mark?' [Kate loves Mark?]. In that case, since no change in word order occurs, it is only by means of stress and tone that we are able to identify the sentence as a question.

In (B), the first sentence is declarative and provides an answer to the first question in (A). The second sentence emphasises that Kate does indeed love Mark, and not whomever else we might have assumed her to love. However, a sentence this verbose is unlikely to occur in everyday speech (or even in written language), be it in English or in German. Instead, one would most likely answer the echo question in (A) simply by restating: Mark!. This is the same for both languages.

In yes–no questions such as (C), English and German use subject-verb inversion. But, whereas English relies on do-support to form questions from verbs other than auxiliaries, German has no such restriction and uses inversion to form questions, even from lexical verbs.

The order of constituents in a phrase can vary as much as the order of constituents in a clause. Normally, the noun phrase and the adpositional phrase are investigated. Within the noun phrase, one investigates whether the following modifiers occur before and/or after the head noun.

• adjective (red house vs house red)
• determiner (this house vs house this)
• numeral (two houses vs houses two)
• possessor (my house vs house my)
• relative clause (the by me built house vs the house built by me)

Within the adpositional clause, one investigates whether the languages makes use of prepositions (in London), postpositions (London in), or both (normally with different adpositions at both sides) either separately (For whom? or Whom for?) or at the same time (from her away; Dutch example: met hem mee meaning together with him).