Most definitions describe a sandwich as one or more fillings placed between, or on top of, bread or a bread-like carrier. In practice that covers an enormous range, from a classic two-slice closed sandwich to open sandwiches served on a single base, to rolls, baguettes and toasted builds. There is genuine debate at the edges — whether wraps, burgers or hot dogs "count" depends on who you ask and sometimes even on local regulations. A more useful, everyday test than counting slices of bread is whether the bread is doing the job of holding food you can comfortably eat by hand. By that measure, the sandwich is one of the most flexible foods in the world.

Every sandwich is built from three roles, even when they overlap. The first is the bread, which provides structure and is itself a major flavour and texture component — fresh, well-chosen bread can make or break the whole thing. The second is the filling, which is the star: the meat, cheese, vegetables or combination that defines what the sandwich actually is. The third is the sauce or condiment, which adds moisture, seasoning and often the acidity that balances richer ingredients. Great sandwiches get all three right and in proportion, rather than overloading the filling and neglecting the bread and sauce. Understanding these three parts is the fastest way to improve any sandwich you build.