For the last 40 years, discussions about the optimal mix of macronutrients in the diet have concentrated on the avoidance of fats, especially saturated fats, and encouraged carbohydrate consumption. The role of dietary protein has been discounted. This booklet chronicles the evolving focus of dietary guidance for Americans from disease prevention to achieving optimal health and the emerging science around the importance of protein. The 2-page summary is a brief synopsis of the booklet.