We can’t attribute the history of tacos to an exact date or really know who made the first taco, Gómez-Rejón says. Even the first cookbook published in Mexico, 1831’s El Cocinero Mexicano, doesn’t mention tacos or tortillas. While the cookbook became known for taking a strong nationalist stance and delineating native Mexican food from colonial influence, that influence still reigned strong at the time.

But in the years preceding the Mexican Revolution, which began in 1910, questions emerged about what it meant to be truly Mexicano—and, not coincidentally, the first taquerias opened in Mexico City. “The first taco recipes in print date to the late 1930s, when Josefina Velázquez de León, a cooking instructor and author who traveled the country collecting regional recipes from female home cooks, documented what Mexicans across the country really ate,” Gómez-Rejón says. “So we don’t see a published taco recipe until the 1930s, but people in Mexico had been eating them, and all of their regional variations, for centuries.”

“Every culture has some sort of dish consisting of a filling wrapped in dough,” says Gómez-Rejón. South America has its empanadas; the Middle East has stuffed pitas; Europe has its crepes and blintzes. So what differentiates a taco from those savory bites? “What makes a taco a taco is the tortilla,” she says. Pair that tortilla with a filling—traditionally meat, fish, beans, and vegetables in varying combinations—and you’ve got a taco.

From there, what makes a taco a taco varies by the aficionado. Some say a taco can’t be called a taco unless the tortilla is made of corn (more on that below). Gómez-Rejón says she believes that “a taco isn’t a taco without a really good salsa.” As for what ingredients are in taco seasoning—whether made from scratch or picked up premade—look to paprika, chili powder, cumin, salt, onion powder, and a few other easy-to-find flavorings.

The hard taco shell was marketed to the masses by a fast-food chain in California in the 1950s. While hard shells had been made by Mexicans before, they were always fried to order so as to guarantee freshness. “In the fast-paced U.S., this was not going to fly,” Gómez-Rejón says. Frying to order took too long, so the chain’s founder marketed the pre-fried shells—making ersatz “Mexican food” available to Americans of any ethnicity regardless of proximity to Mexican American communities.

But this has changed. “Immigrants’ culinary traditions have been embraced in the U.S., and taco trucks and taquerias selling everything from tacos al pastor to barbacoa and carnitas—similar to what you can find anywhere in Mexico—have popped up in cities all over the country,” Gómez-Rejón says. “Today you can find tacos with Asian and Polish flavors and every flavor in between. The taco has and will continue to evolve.”