This letter transmits the briefing in response to the National Defense Authorization Act for Fiscal Year 2010, which required a report on rare earth materials in the defense supply chain to the U.S. Senate and U.S. House of Representatives. Contents: Introduction; Objectives, Scope, and Methodology; Background; Summary; Objective 1: Current and Projected Availability; Objective 2: Defense System Dependency; Objective 3: Department of Defense Identified Risks and Actions; Agency Comments; Points of Contact. Charts and tables.