Basic importing information:

www .cbp.gov/trade/basic-import-export

 Government publications :

http://www.cbp.gov/document/publications/importing-united-states#

And select the  Importing into the U.S.pdf

C. Zimmerman, Inc.

C-TPAT: Customs-Trade Partnership Against Terrorism

http://www.cbp.gov/border-security/ports-entry/cargo-security/c-tpat-customs-trade-partnership-against-terrorism