This chapter examines the role of whole grains and refined grains in health, longevity, and chronic disease prevention and describes the nutrient composition of grains and pseudograins—wheat, corn, oats, rice, amaranth, buckwheat, and quinoa—and their significance as dietary staples.  It explains how food processing removes fiber and micronutrients from whole grains, and most people don’t eat enough.  The chapter highlights the beneficial role of oats in lowering LDL cholesterol, in part due to beta-glucan.  It discusses wheat, gluten, and gluten-related disorders like Celiac disease and wheat allergy and combats misinformation about gluten-free diets, explaining the role of FODMAPs and amylase-trypsin inhibitors (ATIs).  It discusses the benefits of whole grains over refined grains, which boost blood sugar and contribute to heart disease and diabetes when part of a Western diet filled with ultra-processed foods (UPFs).  It concludes with tips for identifying whole grains, including reading food labels and ingredients.