Since 2001 Sweden has been a member of the Schengen Area which allows EU citizens from other EU/Schengen member countries to travel through “borderless” areas of Europe. This means that citizens of the member EU countries only need ID such as National ID cards [link to What is a National ID and why is it different from a Swedish ID card]and passports without the need for visas or permits.
The agreement was signed in 1985 by 5 European countries, France, Germany, Luxemburg, Belgium and The Netherlands. It was designed to create an area within Europe that would gradually abolish internal borders and tighten up external borders. Since 1985 a further 21 European members have become members of the Schengen Area.
The countries listed under the Schengen Agreement [http://www.schengenvisainfo.com/schengen-visa-countries-list/]
Who needs a Schengen Visa when they are travelling?[http://www.schengenvisainfo.com/who-needs-schengen-visa/]