Why has diagnostic testing, and in particular diagnostic imaging, increased to such a high level in the United States? I would argue that it is a combination of our medical culture (and our human nature) to eliminate uncertainty, scientific and technical advances leading to new and improved noninvasive tests, substantial barriers to evaluating the value of each test, and patient preference. Combined, these factors have likely contributed to an exponential growth in testing (particularly imaging) in recent years and are the areas that must be addressed if we wish to provide more efficient care.