When the English court has to decide whether a marriage is valid, foreign elements may be involved: one or both of the spouses may be of overseas origin, or the marriage may have been celebrated in a foreign country. This chapter considers which law applies to determine the validity of such marriages. For choice of law purposes, rules about the validity of marriage are divided into two classes: those concerned with formal validity and those concerned with essential validity or capacity to marry. Rules of formal validity lay down the way in which a marriage must be celebrated (for example, to ensure publicity and proof of marriage). Rules of essential validity or capacity are concerned with the permissibility of the marriage relationship itself — whether the parties ought to be allowed to marry each other (or at all). The chapter also discusses the application of the doctrine of renvoi and rules for same-sex marriages, civil partnerships, and polygamous marriages.