To add to MikeDC's list of books, there's one basic healthcare primer that served me incredibly well before my interviews:
Understanding Health Policy, K. Grumbach, MD and T. Bodenheimer, MD
This was an extremely well-organized and well-written introduction to the major health policy topics on the table today. They use lots of descriptive examples and vignettes to illustrate the complexity of the issues, which was helpful. I can't recommend this book more highly.
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