Nondestructive testing (NDT) for flaws in materials and structures has undergone an evolutionary change over the past 50 years. In the U.S. it has moved from a testing strategy (NDT) with a zero defects requirement to a test and evaluate technology (NDE) based upon damage tolerant design considerations. Here it is assumed that the part will always contain defects but those greater than a critical size, specified by fracture mechanics, will be removed by inspection thereby resetting the part’s service clock. In this talk, events will be identified that were critical in promoting this paradigm shift and in moving on to quantitative NDE (QNDE). A number of major research programs were also initiated to upgrade NDT to meet the new requirements; principal attention in this talk will be given to research highlights initiated in the first of these programs, the DARPA∕AFML Interdisciplinary Program for Quantitative Flaw Definition that was established 35 years ago. Its purpose was threefold: to develop a new core science∕people base for inspection technology that could meet the new requirements, to set the stage for new field—adaptable engineering tools, and to initiate the current continuing series of quantitative NDE (QNDE) meetings. Advances initiated in this program and pursued by many over the years have resulted in a scientific core structure for quantitative NDE (QNDE) based on a linkage of fundamental models of the various measurement processes that are involved in any inspection and∕or technology. These models and their linkage will be discussed and the core structure defined. A new and powerful set of engineering tools—i.e. simulation programs for UT, X‐ray, and EC technologies ‐has also been developed using these models. Applications of these tools will be highlighted and their role in other advanced programs including Structural Health Monitoring and Condition‐Based Maintenance will be noted. Finally, a discussion of visions of future opportunities and directions for QNDE will be given.