This report is the final product of an 18-month study by the Committee on Public Understanding of Engineering Messages, a group of experts on diverse subjects brought together under the auspices of the National Academy of Engineering (NAE). The committee’s charge was to identify and test a small number of messages that appear likely to improve the public understanding of engineering. To fulfill that charge, the committee used the services of professional marketing and communications firms, hired through a competitive request-for-proposals process. Working with the committee, these firms conducted qualitative and quantitative research to collect data and develop messages, themes, and taglines based on that data. This report follows Raising Public Awareness of Engineering, an NAE report published in 2002, which revealed that the engineering community has been spending hundreds of millions of dollars annually to promote the public understanding of engineering with little measurable impact on young people or adults. That study’s committee concluded that the messages being communicated had not been developed in a systematic way and recommended that more effective, consistent messages be developed and used in a coordinated way by organizations interested in enhancing public understanding of the critical role engineers play in today’s world. Given the concerns in the United States about the importance of STEM (science, technology, engineering, mathematics) education to global competitiveness, national security, and quality of life, the current report is especially timely. But messaging is about much more than “priming” the engineering-education pipeline. The vast majority of Americans will never become engineers, but all Americans—young and old—can benefit by having a better understanding of the role engineers play in the creation of technologies. Effective messaging can help raise the level of technological literacy in the general population, a key competency for the 21st century.