The Near-Earth Object Surveyor (NEOS) is currently undergoing preliminary design activities and preparing to enter the detailed design phase of the project. NEO Surveyor is to designed to detect, categorize and characterize NEOs using infrared imaging. The NEOS project responds to National Research Council's report Defending Planet Earth: Near-Earth Object Surveys & Hazard Mitigation Strategies (2010), the U. S. National Near-Earth Object Preparedness Strategy and Action Plan (June 2018), and the objectives of NASA's Planetary Defense Coordination Office (PDCO). The project was identified as a high priority project in the recent NASA Authorization Act. The goals of the NEOS project are to: (1) identify impact hazards to the Earth posed by NEOs (both asteroids and comets) by performing a comprehensive survey of the NEO population; (2) obtain detailed physical characterization data for individual objects that are likely to pose an impact hazard; (3) characterize the entire population of potentially hazardous NEOs to inform potential mitigation strategies by assisting the determination of impact energies through accurate object size determination and physical properties. The mission will make significant progress toward the George E. Brown, Jr. NEO Survey Program objective of detecting, tracking, cataloging, and characterizing at least 90% of NEOs equal to or larger than 140 m in diameter. The project is a collaboration between NASA-JPL, the University of Arizona and industry, with Ball Aerospace notably providing the spacecraft and key instrument elements. This paper will describe the key activities and accomplishments performed by the NEOS Project during the preliminary design phase and describe how these have matured the overall mission.