Lasagna, also known by the plural form lasagne, is a type of pasta made in wide, flat sheets. It originates in Italian cuisine, where it is served in a number of ways , including in broth (lasagne in brodo), but is best known for its use in a baked dish made by stacking layers of pasta, alternating with fillings such as ragù (ground meats and tomato sauce), béchamel sauce, vegetables, cheeses (which may include ricotta, mozzarella, and Parmesan), and seasonings and spices. Typically, cooked pasta is assembled with the other ingredients, topped with grated cheese, and then baked in an oven (al forno): regional variations of this dish are found across Italy.

As with most other types of pasta, the Italian word is a plural form: lasagne (Italian: [laˈzaɲɲe]) meaning more than one sheet of lasagna (UK: /ləˈzænjə/, US: /ləˈzɑːnjə/; Italian: [laˈzaɲɲa]). When referring to the baked dish, regional usage in Italy favours the plural form lasagne in the north of the country and the singular lasagna in the south. The former plural usage has influenced the usual spelling found in British English, while the southern Italian singular usage has influenced the spelling often used in American English. Both lasagna and lasagne are used as singular non-count (uncountable) nouns in English.

In ancient Rome, there was a dish similar to a traditional lasagna called lasana or lasanum (Latin for 'container' or 'pot') described in the book De re coquinaria by Marcus Gavius Apicius, but the word could have a more ancient origin. The first theory is that lasagna comes from Greek λάγανον (laganon), a flat sheet of pasta dough cut into strips. The word λαγάνα (lagana) is still used in Greek to mean a flat thin type of unleavened bread baked for the Clean Monday holiday.

Another theory is that the word lasagna comes from the Greek λάσανα (lasana) or λάσανον (lasanon) meaning 'trivet', 'stand for a pot' or 'chamber pot'. The Romans borrowed the word as lasanum, meaning 'cooking pot'. The Italians used the word to refer to the cookware in which lasagna is made. Later the food took on the name of the serving dish.^{[citation needed]}

Another proposed link or reference is the 14th-century English dish loseyn as described in The Forme of Cury, a cookbook prepared by "the chief Master Cooks of King Richard II", which included English recipes as well as dishes influenced by Spanish, French, Italian, and Arab cuisines. This dish has similarities to modern lasagna in both its recipe, which features a layering of ingredients between pasta sheets, and its name. An important difference is the lack of tomatoes, which did not arrive in Europe until after Columbus reached the Americas in 1492. The earliest discussion of the tomato in European literature appeared in a herbal written in 1544 by Pietro Andrea Mattioli, while the earliest cookbook found with tomato recipes was published in Naples in 1692, but the author had obtained these recipes from Spanish sources.

Lasagna originated in Italy during the Middle Ages. The oldest known written reference to lasagna appears in 1282, in a ballad transcribed by a Bolognese notary, "Pur bii del vin, comadre, e no lo temperare" ('Just drink some wine, my woman, and do not dilute it'), part of the Memoriali Bolognesi (lit. 'Bolognese Memorials'):

Giernosen le comadre trambedue a la festa,
de gliocch'e de lasagne se fén sette menestra

Both women went to the festival,
and had seven portions of gnocchi and lasagne