"Yeast, baking soda, and baking powder are all leavening agents used in baking. Yeast reacts with sugar, causing it to ferment. The fermentation then results in the production of carbon dioxide. The carbon dioxide gets trapped in bread dough and becomes little air bubbles responsible for making bread rise. Yeast is ideal for bread-making, because the rise happens before baking — giving you more control over the finished product — but it does require time. "For cakes, muffins, pancakes, or any other baked goods that go straight into the oven without rising, baking soda or baking powder are the way to go. Baking soda (scientific name: sodium bicarbonate) also creates carbon dioxide, and although it doesn't need resting time to start working, it does need acid. Baking soda is great for recipes that have built-in acidic elements, like lemon or buttermilk — without them, baking soda leaves behind a distinctive taste. "Baking powder is baking soda mixed with a few extra ingredients, including an acid. When you're baking a recipe that doesn't call for any acids, baking powder provides the rising power of baking soda and takes care of the chemistry part for you. Baking powder is only fully activated by heat, which is why a cake rises in the oven and not on your countertop, the way bread does." Thanks, Yasmina!