In syntax, verb-second (V2) word order is a specific restriction on the placement of the finite verb within a given sentence or clause. The V2 principle requires the finite verb (the verb inflected for person) to appear in the second position of a declarative main clause or the given clause, and the first position is occupied by a single major constituent, which functions as the clause topic.

V2 word order is common across the Germanic languages and is also found in Indo-Aryan Kashmiri, Northeast Caucasian Ingush, Uto-Aztecan O'odham and fragmentarily in Rhaeto-Romansh Sursilvan. Among members of the Germanic family, English, which has predominantly SVO instead of V2 order, is an exception (although certain vestiges of the V2 phenomenon can also be found in English). Germanic languages and Kashmiri differ with respect to word order in embedded clauses.

Most Germanic languages do not normally use the V2 principle in embedded clauses, except in a certain semantic type of clause with certain verbs. Thus, German, Dutch and Afrikaans revert to VF (verb final) word order in embedded clauses. Two Germanic languages, Yiddish and Icelandic, allow V2 in all declarative clauses: main, embedded, and subordinate. Kashmiri has V2 in 'declarative content clauses' but VF order in relative clauses.

In linguistics, word order typology is the study of the order of the syntactic constituents of a language, and how different languages can 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 – the relative order of subject, object, and verb; the order of modifiers (adjectives, numerals, demonstratives, possessives, and adjuncts) in a noun phrase; and the order of adverbials.

Some languages use relatively restrictive word order, often relying on the order of constituents to convey important grammatical information. Others—often those that convey grammatical information through inflection—allow more flexibility, which can be used to encode pragmatic information such as topicalisation or focus. Most languages, however, have a preferred word order, and other word orders, if used, are considered "marked".

Most nominative–accusative languages—which have a major word class of nouns and clauses that include subject and object—define constituent word order in terms of the finite verb (V) and its arguments, the subject (S), and object (O).