A blueprint is any exact or detailed plan or outline of a product, program, project or vision; it is detailed plan of action; a model or prototype; a detailed operational plan for undertaking a project Literally, a blueprint is a two-dimensional set of drawings that provides a detailed visual representation of how an architect wants a building to look. Blueprints typically specify a building's dimensions, construction materials, and the exact placement of all its components.

Blueprints were first introduced in the 19th century, to allow the reproduction of documents, particularly drawings used in industrial products and construction. Blueprints are generally recognizable from their blue background and light-colored lines. They create an accurate negative reproduction of the original using a contact print process on light-sensitive sheets. Before this, reproductions were created using a photolithographic process, or by hand-tracing, both of which were expensive and time consuming.

Blueprints were developed in 1861 by French chemist Alphonse Louis Poitevin, who discovered that ferro-gallate becomes an insoluble, permanent blue when exposed to light. If it is coated onto paper (or a similar sheet material such as imitation vellum or polyester film) in an aqueous solution and then dried, (at which point it is yellow) it can be used to accurately reproduce large- scale translucent documents such as drawings.