A government witness's prior statements that the government must produce to the defense after the government witness's direct examination ends during:

(Fed. R. Crim. P. 26.2.)

The term originated with Jencks v. United States, in which the US Supreme Court held that the government must produce certain statements of its witnesses to the defense (353 U.S. 657 (1957)). The holding was later codified in the Jencks Act (18 U.S.C. § 3500). Subsequently, Rule 26.2 was enacted, which currently governs the production of witness statements. Practitioners, however, continue to refer to these statements as "Jencks material" and to the obligations to produce them as "Jencks obligations." Practitioners may also refer to these statements as "3500 material."

Rule 26.2 also requires production of a defense witness's statements in the same manner as a government witness's statements. This is commonly referred to as "reverse-Jencks material."