The United States Nuclear Regulatory Commission is consolidating the capabilities of four of its thermal-hydraulic neutronics codes, i.e., TRAC-P, TRAC-B, RELAP-5, and RAMONA, into a single state-of-the-art analysis code, TRAC-M. Qualification testing will be conducted to ensure that TRAC-M achieves its design requirements. Code validation is an essential element of qualification testing; it is the process whereby satisfaction of the design requirements is demonstrated. A comprehensive validation test matrix is required to qualify TRAC-M for its intended applications. In this three-part paper, the validation test matrix for the consolidated TRAC-M code is presented. Part I provides an overview of the principles guiding development of the validation test matrix and lays the foundation for presentation of the tests selected for the validation test matrix in Parts II and III.