Book excerpt: Spacecraft depend on electronic components that must perform reliably over missions measured in years and decades. Space radiation is a primary source of degradation, reliability issues, and potentially failure for these electronic components. Although simulation and modeling are valuable for understanding the radiation risk to microelectronics, there is no substitute for testing, and an increased use of commercial-off-the- shelf parts in spacecraft may actually increase requirements for testing, as opposed to simulation and modeling. Testing at the Speed of Light evaluates the nation's current capabilities and future needs for testing the effects of space radiation on microelectronics to ensure mission success and makes recommendations on how to provide effective stewardship of the necessary radiation test infrastructure for the foreseeable future.