Avocado toast is an open sandwich consisting of toasted bread topped with mashed avocado, plus any of a variety of spices and flavorful ingredients; the most popular include salt and black pepper, lemon juice, or other citrus flavors, olive oil, hummus, vinegar, red pepper, feta, duqqa, and tomato.

Avocado toast became a food trend in the 2010s; however, the preparation has appeared on café menus since at least the 1990s. There have been several debates about where the dish first appeared on menus. Following avocado toast's elevation to trend status, the act of ordering avocado toast at a café was criticized as a symbol of frivolous spending, along with the environmental impact of shipping the fruit from subtropical growing regions.

Avocados are grown around the world in tropical climates, historically in Mesoamerica and Northern South America. The trees and fruit have been cultivated by pre-Columbian civilizations from South Central Mexico for nearly 9,000 years.

Sliced or mashed avocado has been eaten on some sort of bread, flatbread, or tortilla (often heated or toasted) for centuries, before any documented or written history. In Chile, avocado on marraqueta or "pan con palta" or "tostadas con palta" is a common breakfast documented in a 1926 cookbook.

The consumption of avocados on bread or toast has been reported in various sources from the late 19th century onward however, there has been debate over when the dish first appeared on menus. In the San Francisco Bay Area, people have been eating avocado toast since at least 1885. In 1915, the California Avocado Association described serving small squares of avocado toast as an appetizer. In an article published in The New Yorker on 1 May 1937, titled "Avocado, or the Future of Eating", the writer eats "avocado sandwich on whole wheat and a lime rickey." In 1962, an article in The New York Times showcased a "special" way to serve avocado as the filling of a toasted sandwich. According to The Washington Post, chef Bill Granger may have been the first person to put avocado toast on a modern café menu in 1993 in Sydney, although the dish is documented in Brisbane, Australia, as early as 1929. In 1999, food writer Nigel Slater published a recipe for an avocado "bruschetta" in The Guardian. The journalist and editor Lauren Oyler credited Cafe Gitane with bringing the dish to the United States in its "Instagrammable" form, as it grew as a food trend.

Variations include avocado on sweet potato toast, avocado and Vegemite toast, French toast with avocado and Parmesan, avocado toast fingers with soft-boiled eggs, avocado and baked beans on toast, and avocado and feta smash^{[clarification needed]} on toasted rye. Another common variation is toast with smashed avocados, soft-boiled egg, and other toppings, often including hot sauce.

Celebrities such as Gwyneth Paltrow have been credited with the popularization of avocado toast through her recipe book, It's All Good. The dish was popularized on social media, with many food bloggers recreating the dish. Bon Appétit magazine published a recipe for "Your New Avocado Toast" in its January 2015, and by 2016, the dish was being depicted on T-shirts, with the Washington Post calling it "more than just a meal – it's a meme".

Jayne Orenstein of The Washington Post reports, "avocado toast has come to define what makes food trends this decade: It's healthy and yet ever-so-slightly indulgent. It can be made vegan and gluten-free."