A BLT is a sandwich built from bacon, lettuce, and tomato, typically on toasted bread with mayonnaise. The combination became a popular sandwich filling in the United States in the early 20th century, growing out of earlier tea sandwiches that paired bacon with lettuce and tomato.
The bacon is usually thin-sliced and cooked crisp; the lettuce is a crisp variety such as iceberg or romaine, chosen for crunch and a mild, faintly bitter contrast; and the tomato is a ripe, juicy slice that adds sweetness and acidity. Mayonnaise ties the three together with a creamy, tangy note.
Common variations swap in or add a fourth ingredient: a BLAT adds avocado, and turkey or chicken versions are sometimes labeled BLTT or BLCT. A regional version served on Cuban bread is common in South Florida.
A BLT is not the same as a club sandwich, even though both often contain bacon, lettuce, and tomato: a club is a triple-decker built from two bread layers and usually centers on turkey or chicken as its main protein, while in a BLT bacon is the primary protein.