The expression capitulaciones matrimoniales is often translated as “prenuptial (or) antenuptial agreement.” This may be correct in many circumstances, but it should be underscored that the expression can also denote a “postnuptial agreement” entered into after marriage. In effect, capitulaciones matrimoniales traditionally refers to an agreement between the spouses, entered into either before or during the marriage, setting forth the marital property system (régimen económico matrimonial) that will govern their relationaship. As such, it may perhaps be best described simply as a “marital property agreement.”

Briefly, the two most common marital property systems in Spain are régimen de (bienes) gananciales (“community property system”) in which all property acquired during the marriage is jointly owned by both spouses, and régimen de separación de bienes (“separate property system”) in which during the marriage spouses own property separately. In marriages governed by the community property system, bienes gananciales (often shortened to “gananciales”) refers to jointly-owned “community property,” while bienes privativos describes the “separate property” that each spouse owned before marriage or acquires by gift or inheritance during the marriage, and which is not considered a part of jointly-owned marital property.

Other expressions describing this type of spousal agreement include capítulos matrimoniales, pactos matrimoniales and pactos capitulares. In other respects, the term capitulaciones paramatrimoniales is sometimes used in Spain to denote the cohabitation agreement that nonmarital couples sign when registering a nonmarital union (unión de hecho).

The community property system (régimen de gananciales) is the “default system” (régimen por defecto) in the Spanish regions governed by the Civil Code. A separate property system (régimen de separación de bienes) is the default system in Catalonia and the Balearic Islands. Default marital property systems in other regions include comunicación foral de bienes in certain territories of the Basque Country, consorcio conyugal in Aragón, and sociedad conyugal de conquistas in Navarre.

Common law countries traditionally observe strict separate property rules, with the exception in the US of the community property systems in Arizona, California, Idaho, Louisiana, Nevada, New Mexico, Texas, Washington and Wisconsin. (Alaska has an “opt-in” system allowing spouses the option to make their marital property community property). Collectively these are generally known as “community property states” in contrast to the other “separate property states,” sometimes also referred to as “common law states.” In community property states “community property” is normally defined as all property acquired during the marriage, including money and wages, and items purchased with that money. “Separate property” is usually property owned by either spouse before marriage, acquired by gift or inheritance, or purchased with separate funds during the marriage.

Read more here.