Tex-Mex — the hard-shell tacos, yellow cheese, and combination platters familiar across the US — is a genuine regional cuisine in its own right, but it's a Texas-Mexico border hybrid, not a representative sample of Mexican cooking. Mexico's actual culinary range runs far deeper, shaped heavily by Indigenous traditions that predate Spanish colonization by thousands of years.
The Nahua — descendants of the Aztec and related peoples of central Mexico — gave the world foundational techniques still central to Mexican cooking today: nixtamalization (treating corn with lime to make it more nutritious and grindable, the basis of every corn tortilla), mole (a complex sauce built from dozens of ingredients including chili and often chocolate), and the use of ingredients like tomato, avocado, and vanilla that didn't exist in European cooking before contact with the Americas.
Yucatecan cooking, rooted in Maya tradition, is distinctly different from central Mexican food — achiote (annatto seed paste) gives dishes like cochinita pibil (slow-roasted, achiote-marinated pork, traditionally cooked in an underground pit) their signature reddish color and earthy flavor, and sour orange stands in for lime as the region's dominant souring agent.
Oaxaca, home to both Zapotec and Mixtec traditions, is often called Mexico's culinary capital — it's the birthplace of the seven moles of Oaxaca (each a distinct, painstakingly built sauce), tlayudas (large, crisp toasted tortillas topped like an open sandwich), and chapulines (toasted grasshoppers, a genuinely traditional protein source, not a novelty).
Nahua, Maya, Zapotec and Mixtec traditions only begin to map Mexico's range — Otomi cooking and dozens of other Indigenous and regional traditions each contribute their own staples to what gets flattened, outside Mexico, into a single "Mexican food" category.