Multiyear Procurement (MYP) and Block Buy Contracting in Defense Acquisition: Background and Issues for Congress [Updated June 24, 2020] [open pdf - 1MB]
From the Introduction: "This report provides background information and issues for Congress on multiyear procurement (MYP) and block buy contracting (BBC), which are special contracting mechanisms that Congress permits the Department of Defense (DOD) to use for a limited number of defense acquisition programs. Compared to the standard or default approach of annual contracting, MYP and BBC have the potential for reducing weapon procurement costs by a few or several percent."
CRS Report for Congress, R41909
Congressional Research Service: https://crsreports.congress.gov/