Tortillas are made from corn or wheat flour, mixed with water and a little salt, rolled flat and cooked quickly on a hot pan. A good tortilla is soft, warm and slightly spongy. In Mexico, you tear off pieces with your hands and use them like an edible spoon.
Almost every Mexican town has its own favourite taco. Tacos al pastor are made with marinated pork roasted on a spinning skewer - they often come with a slice of fresh pineapple. Tacos de pescado, fish tacos, are popular near the coast. Tacos de carnitas are slow-cooked pork until it pulls apart in your fingers.
Tacos are usually served with sprinkled chopped onion and fresh coriander leaves, plus a wedge of lime to squeeze over the top, and a small bowl of salsa - tomato, chilli and herbs - on the side. The whole meal is usually eaten with your hands.
Tacos have travelled around the world. You'll find Mexican taco restaurants in every big city - in London, Tokyo, Sydney, Berlin. But to Mexicans, the best tacos still come from a small street stall in their own neighbourhood, where the cook has been making the same recipe for years.