The bulk of federal regulations pertaining to immigration reside in Title 8 of the CFR, entitled "Aliens & Nationality." These regulations can be found in the CFR databases of either the LexisNexis or Westlaw. In addition, up-to-date versions of Title 8 of the CFR can be found on the GPO FDsys website by clicking HERE
Often, legislation and regulations are explained through agency policy memorandum. Finding such policy statements can be helpful in immigration research or practice.
Search the ICE website:
The Immigration and Customs Enforcement website contains a wide array of agency memoranda burried in their content. Conduct a search of the page for 'memorandum' to pull up their offereings.
Search the USCIS website:
The United States Customs and Immgration Website posts many of their agency memoranda. Most can be found HERE