The rulebook governing all FBI agents' activities, in unredacted form for the first time. This is the 2011 edition, which remains the baseline document today, although the FBI recently released some updates from 2013.

See Document

Hidden Loopholes Allow FBI Agents to Infiltrate Political and Religious Groups

Cora Currier

Beneath the FBI's redaction marks are exceptions to rules on "undisclosed participation."

National Security Letters Demand Data Companies Aren't Obligated to Provide