Take anything delicious, wrap it in a warm corn or flour tortilla and you can call it a taco. There are few foods with such rich history and creative interpretation.

Tacos have probably been around as long as tortillas have, since the flatbread base is the food's defining characteristic. Archaeological evidence suggests that maize has been part of the Mesoamerican diet since 10,000 B.C., but the first written evidence of the corn flatbread came from Spain during the time of Cortes in the early 16th century. The Spanish gave the flatbread the name tortilla. They also introduced wheat flour to the Mesoamerican diet, resulting in flour tortillas.

Mexican tacos themselves are amazingly diverse. But as tortillas became more ubiquitous in the United States, cooks and chefs began to realize that taco filling left endless room for the culinary imagination. In the past two years, Pittsburgh, like much of the country, has seen a significant increase in taco options, both authentic and creative.

In Mexico, tacos are usually sold on the street, casual snacks to be eaten as soon as they're cooked, simply garnished with cilantro, onion, lime and perhaps salsa. Since he closed his restaurant Taco Loco on the South Side, Edgar Alvarez has operated a taco stand in front of Reyna's Foods in the Strip District, serving freshly prepared tacos on Reyna's corn and flour tortillas, as well as agua frescas and churros daily from 10 a.m. to 3:30 p.m.

Tacos options vary, but often include steak, chicken, beef, roast pork, beef tongue (lengua), all $3 or two for $5, as well as shrimp and fish, $3 each. He also makes the salsas for sale inside Reyna's alongside the stacks of freshly prepared corn and flour tortillas.

Tortillas may be available in every grocery store these days, but once you've tried freshly prepared versions like these, you'll have a hard time settling for preservative-filled, refrigerated options.

About a third of Mr. Alvarez's South Side customers have tracked him down to the Strip District stand, but he also attracts new taco lovers every day.

"A lot of people here in the Strip, they start with one taco and then right away they come back for another," said Mr. Alvarez, who has noticed a growing appreciation for authentic tasting tacos over the nine years he has been preparing Mexican food in Pittsburgh.

On weekends, people have been flocking to Las Palmas Carniceria y Supermercado in Brookline for the freshly made tacos and other traditional foods. Primarily a Mexican grocery and butcher shop, Las Palmas sells hot food Fridays and Saturdays, starting around 2 p.m., and Sundays starting around noon. Options usually include roast pork, carne asada, chorizo and rib eye tacos.

For a sit-down experience, Taqueria Mexico City is almost certainly the most popular spot in town, if its expansion rate is any indicator. The restaurant was so successful at its Smithfield Street Downtown location that two years ago it expanded to a second spot a few blocks away on Wood Street. Now it's opened a South Side location with an even more extensive menu, including a lot more tacos.

Mexican tacos have gained so much attention that even Taco Bell -- no one's idea of an authentic Mexican meal -- is trying to get in on the action. Just last week the fast food chain introduced Cantina tacos, "based upon authentic Mexican Street Tacos, which are all about the simple, but high quality ingredients," according to the press release. The new tacos are served on warm corn tortillas topped with either grilled chicken, carne asada steak or carnitas shredded pork, with a chopped onion and cilantro blend and served with a wedge of lime.

Tacos seem to be the ambassadors of Mexican cuisine, winning hearts and minds (and stomachs) even in areas without substantial opportunities for exploring Mexican cuisine. But the popularity of tacos now extends far beyond the boundaries of nominally Mexican food.

Fusion tacos most likely owe their current popularity to a single Los Angeles food truck -- the Kogi truck. Founders Mark Manguera, Caroline Shin-Manguera and chef Roy Choi started serving Korean Mexican tacos from a truck in 2008, and that single truck has grown to a fleet of five. They first gained nationwide attention for their effective use of Twitter to help people find the truck -- @kogibbq has more than 70,000 followers. Now they've inspired dozens of copycats and innovators across the country.

On a recent trip to L.A., I found more than a dozen popular food trucks gathered in a parking lot in the beach town of Venice for their version of first Friday. When the Kogi truck arrived (fashionably late) the line formed immediately. Some checked the truck's Twitter feed as they waited to see the daily specials, such as the Thai Eye'd burritos. A popular choice is the short rib taco -- soy-marinated short rib topped with salsa roja, onion and cilantro and a crunchy salad dressed in chile-soy vinaigrette ($2).

Many of the trucks were serving their take on fusion tacos, like the dim sum truck (@dimsumtruck on Twitter) which had Peking duck alongside lots of traditional dim sum, such as pork and shrimp shu mai dumplings and baked barbecued pork buns.

In Pittsburgh, if you're looking for Latin-Asian fusion, you go to Tamari in Lawrenceville. Try the Korean-style marinated steak tacos served on a grilled, house-made flour tortilla with roasted corn and a slightly spicy roasted red pepper sauce ($10) and the pulled pork tostada; moist pork topped with a spicy slaw that owner Allen Chen described as "our version of kimchi" ($8).

If you're looking to test the boundaries of the taco, there's only one place to go: Yo Rita on the South Side. Eric Wallace took over the chef job from Kevin Sousa this spring and has put his own mouthwatering spin on small plates and tacos.

These are best described as "chef-inspired," a mix of flavors, cuisines and playful combinations of high and low culinary influences. The menu changes with the seasons, and sometimes more often than that. Crispy eggplant, deep fried until puffy and crunchy was topped with crunchy hot fries. A bit of sweet chile and avocado were hidden beneath the overflowing pile of eggplant, lining the warm flour tortilla ($6). Braised chicken is similarly tongue-in-cheek, sauced with chipotle bbq and sprinkled with quesa fresca, then garnished with some cool ranch Doritos ($4). The escolar taco has a lighter, more delicate flavor profile of bok choy, shitake mushrooms, aji Amarillo chiles, sweet soy and plenty of cilantro ($7).

They can be extremely sophisticated as well, like a cold taco of freshly picked Dungeness crab with a sweet cantaloupe slaw ($9), or meltingly tender braised pork belly with a sour cherry relish ($6).

Hard-to-find proteins also pop up regularly, such as an incredible taco turtle special ($8; it tastes like a freshwater fish but with a meatier texture) and recently a curried goat taco that I am dying to try (for specials, follow on Twitter @YoRitaSouthSide).

Yo Rita's many charms include quality cocktails, seasonally inspired cold soups and salads, know-ledgeable service and an impressively low price tag. Although not quite the $1-$3 of most authentic taco joints, fusion tacos have allowed chefs to create incredibly sophisticated food with high quality ingredients at prices that almost anyone can afford.

The Great Recession had a lot of painful effects, but we can all be grateful for the culinary creativity it inspired.

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