There are important variations among the various regions of Spain and Spanish-speaking America. In Spain the North Castilian dialect pronunciation is commonly taken as the national standard (although the characteristic weak pronouns usage or laísmo of this dialect is deprecated).
Spanish has three second-person singular pronouns: tú, usted, and in some parts of Latin America, vos (the use of this form is called voseo). Generally speaking, tú and vos are informal and used with friends (though in Spain "vos" is considered a highly exalted archaism that is now confined to liturgy). Usted is universally regarded as the formal form, and is used as a mark of respect, as when addressing one's elders or strangers. The pronoun "vosotros" is the plural form of "tú" in most of Spain, although in the Americas (and some particular southern-Spain cities such as Cádiz) it is replaced with "ustedes." It is remarkable that the informal use of "ustedes" in southern Spain does not keep the proper pronoun-verb relationship: while the formal form of "you go" would be "ustedes van", in Cádiz the informal form would be constructed as "ustedes váis", making use of the second person of the plural instead of the third (which constitutes the formal construction).
Vos is used extensively as the primary spoken form of the second-person singular pronoun in various countries around Latin America, including Argentina, Costa Rica, Ecuador, El Salvador, Guatemala, Honduras, Nicaragua, Paraguay and Uruguay. In Argentina, Uruguay, and increasingly in Paraguay, is it also the standard form used in the media, whereas media in other voseante countries continue to use usted or tú. Vos may also be present in other countries as a limited regionalism. Its use, depending on country and region, can be considered the accepted standard or reproached as sub-standard and considered as speech of the ignorant and uneducated. The interpersonal situations in which the employment of vos is acceptable may also differ considerably between regions.
Spanish forms also differ regarding second-person plural pronouns. The Spanish dialects of Latin America have only one form of the second-person plural; ustedes (formal/familiar). Meanwhile, in Spain there are two; ustedes (formal) and vosotros (familiar/informal).
The RAE (Real Academia Española), in association with twenty-one other national language academies, exercises a controlling influence through its publication of dictionaries and widely respected grammar guides and style guides. In part due to this influence, and also because of other socio-historical reasons, a neutral standardized form of the language (Standard Spanish) is widely acknowledged for use in literature, academic contexts and the media.