Protects the "homeland". Cabinet-level department started by the Bush administration after the September 11 attacks, with the first Secretary being Tom Ridge, who was followed by Michael Chertoff. Agencies included in the DHS are the Secret Service, the Coast Guard, the Transportation Security Administration, and several lesser-known groups.
This site mainly concentrates on Immigration and Customs Enforcement (ICE) and, to a lesser extent, the Citizenship and Immigration Service (USCIS). The first - lately run by Julie Myers - concentrates on looking like they're enforcing our laws at the same time as not really enforcing our laws in order to maintain a ready supply of cheap labor for crooked businesses.