The BLT is still the second-most popular sandwich in the United States (the simple ham sandwich is first).
The BLT, (Bacon, Lettuce and Tomato sandwich) became popular when fresh lettuce and tomatoes became available year round with the rapid expansion of supermarkets after World War II.
A BLT is best when made at home, rather than ordered at a restaurant. The bacon must be fresh cooked and crisp, I like maple cured and smoked bacon. While the bacon is draining on paper towels, toast the bread and slice a ripe, but not too juicey, beefsteak tomato. Make the sandwich with crisped Romaine or Bibb lettuce and some mayonnaise.
Text taken from http://www.foodreference.com/html/fblt.html