From the Summary: "When President George W. Bush announced his principles for immigration reform in January 2004, he included an increase in permanent immigration as a key component. President Bush has stated that immigration reform is a top priority of his second term and has prompted a lively debate on the issue. Bills to revise permanent admissions are being introduced, but only one has had legislative action thus far in the 109th Congress. A provision in P.L. [Public Law] 109-13 (H.R. 1268, the emergency FY2005 supplemental appropriation) makes up to 50,000 employment-based visas available for foreign nationals coming to work as medical professionals [...] Four major principles underlie current U.S. policy on permanent immigration: the reunification of families, the admission of immigrants with needed skills, the protection of refugees, and the diversity of admissions by country of origin. These principles are embodied in the Immigration and Nationality Act (INA). The INA specifies a complex set of numerical limits and preference categories that give priorities for permanent immigration reflecting these principles. Legal permanent residents (LPRs) refer to foreign nationals who live lawfully and permanently in the United States."
CRS Report for Congress, RL32235
U.S. Department of State: http://fpc.state.gov/