A traveler visiting the Schengen area can acquire a visa legally admissible in all Schengen area states by contacting the consulate of the traveler's main destination country with the appropriate paperwork. If there is not a main destination, contact the consulate of the intended first country of entry.
The Schengen area is a list of countries adhering to the eponymous Schengen agreement. Some lists include the microstates that have abolished border controls but are not de jure signatories of to the Schengen agreement as part of the Schengen area. A holder of a Schengen visa can generally visit these microstates without the preparation or additional visas required for travel to countries that have not signed the Schengen agreement.
Not all members of the Schengen area are members of the European Union. The opposite is also true: some members of the EU are not members of the Schengen area. Both the United Kingdom and the Republic of Ireland opted out of the Schengen agreement, while the EU has Bulgaria and Romania scheduled to join the Schengen area in the near-future, as of 2015. Iceland, Liechtenstein, Norway and Switzerland are signatories of the Schengen agreement and accept Schengen visas, but they are not members of the European Union.