Grant Achatz (/ˈækɪts/ AK-its) (born April 25, 1974) is an American chef and restaurateur often recognized for his contributions to molecular gastronomy or progressive cuisine. Achatz has won numerous awards, including Food and Wine's "best new chefs" award in 1998, "Rising Star Chef of the Year Award" for 1999, "Best Chef in the United States" for 1998, a 2003 "Who's Who Inductee" from the James Beard Foundation, and a Jean Banchet Lifetime Achievement Award in 2026. His Chicago restaurant Alinea has won numerous accolades.

Achatz was born on April 25, 1974, in St. Clair, Michigan. He grew up in a family of restauranteurs. His parents, Grant Achatz Sr. and Barbara Jean Achatz, owned and operated the Achatz Depot (later renamed the Achatz Family Restaurant). It was a casual diner specializing in breakfast staples and comfort food like burgers and meatloaf. His interest in the culinary arts began early, as he spent much of his childhood in the family kitchen, eventually working as a short-order cook flipping eggs during his teenage years.

In 1992, Achatz moved to New York to attend The Culinary Institute of America in Hyde Park. While at the CIA, he focused on building a classical foundation, which he later cited as essential for his transition into the complex techniques of modernist cuisine. He graduated in 1994 with an Associate in Occupational Studies degree.

Following graduation in 1994, Achatz moved to Chicago and landed a position at the renowned Charlie Trotter's. Later, he worked at Thomas Keller's highly acclaimed restaurant, The French Laundry, in Yountville, California. Achatz spent four years at The French Laundry, rising to the position of sous chef.

In 2001, Achatz advanced to position of Executive Chef at Trio in Evanston, Illinois, which at the time of his arrival had a four-star rating from the Mobil Travel Guide. Over the next three years, with Achatz at the helm, Trio's reputation soared, and in 2004 the restaurant was rewarded with a fifth star from Mobil, becoming one of just 13 restaurants so honored at the time.

In 2005, Achatz went out on his own, opening Alinea in Chicago's Lincoln Park neighborhood with Nick Kokonas. The restaurant is located up the block from the famed Steppenwolf Theatre Company and is housed in a modest gray brick building which bears no external markings beyond its street number. Inside, the restaurant has no bar, no lobby and seats just 64 guests. Achatz serves diners a small-course tasting menu, consisting of approximately 18 courses. After less than two years of operation, the Mobil Travel Guide bestowed its Five Star Award on Alinea, making Alinea one of just 16 restaurants nationwide to rate five stars for 2007.

In October 2006, Gourmet magazine named Alinea the best restaurant in America in its feature on "America's Top 50 Restaurants". In 2007, Restaurant magazine added Alinea to its list of the 50 best restaurants in the world at number 36, the highest new entry of the year. Alinea moved up the list to number 21, to number 10 in 2009, then to number 7 for 2010, when it was also the highest ranked North American restaurant honored. Alinea maintained its top North American position for 2011, while moving up one position overall to 6th best restaurant in the world. In 2012, Alinea came down one spot on the list. Per Se was in 6th place, thus making Alinea the 2nd best restaurant in the U.S. and 7th overall.

In November 2009, Achatz and his Alinea team designed the menu for Ikarus, a restaurant in Salzburg, Austria, which brings in a top chef from a different restaurant each month to design the menu for that month and train the staff.