<p>Microbiological testing helps clinicians identify pathogens and optimize treatment. However, infection may be misdiagnosed when a “positive” culture represents colonization or contamination. Misdiagnosis of infection may delay correct diagnosis, prompt inappropriate antibiotic use, and result in patient harm. Diagnostic stewardship can improve the appropriate use of microbiological tests and cultures. As diagnostic tests have proliferated, our reliance on tests for diagnosis has increased, even as our knowledge of test characteristics has decreased. Consideration of the mental models that contribute to overtesting can help us identify strategies to combat the “culture of culturing.”</p>