A manuscript (abbreviated MS for singular and MSS for plural) was, traditionally, any document written by hand or typewritten, as opposed to mechanically printed or reproduced in some indirect or automated way. More recently, the term has come to be understood to further include any written, typed, or word-processed copy of an author's work, as distinguished from the rendition as a printed version of the same.

Before the arrival of prints, all documents and books were manuscripts. Manuscripts are not defined by their contents, which may combine writing with mathematical calculations, maps, music notation, explanatory figures, or illustrations.

The word "manuscript" derives from the Latin: manūscriptum (from manus, hand and scriptum from scribere, to write), and is first recorded in English in 1597. An earlier term in English that shares the meaning of a handwritten document is "hand-writ" (or "handwrit"), which is first attested around 1175 and is now rarely used. The study of the writing (the "hand") in surviving manuscripts is termed palaeography (or paleography). The traditional abbreviations are MS for manuscript and MSS for manuscripts, while the forms MS., ms or ms. for singular, and MSS., mss or mss. for plural (with or without the full stop, all uppercase or all lowercase) are also accepted. The second s is not simply the plural; by an old convention, a doubling of the last letter of the abbreviation expresses the plural, just as pp. means "pages".

A manuscript may be a codex (i.e. bound as a book), a scroll, or bound differently or consist of loose pages. Illuminated manuscripts are enriched with pictures, border decorations, elaborately embossed initial letters or full-page illustrations.

The mechanical reproduction of a manuscript is called facsimile. Digital reproductions can be called (high-resolution) scans or digital images.

Before the inventions of printing, in China by woodblock and in Europe by movable type in a printing press, all written documents had to be both produced and reproduced by hand. In the west, manuscripts were produced in form of scrolls (volumen in Latin) or books (codex, plural codices). Manuscripts were produced on vellum and other parchment, on papyrus, and on paper.

In Indian Subcontinent and Southeast Asia, palm leaf manuscripts, with a distinctive long rectangular shape, were used dating back to the 5th century BCE or earlier, and in some cases continued to be used until the 19th century. In China, bamboo and wooden slips were used prior to the introduction of paper. In Russia, birch bark documents as old as from the 11th century have survived.

Paper spread from China via the Islamic world to Europe by the 14th century, and by the late 15th century had largely replaced parchment for many purposes there. When Greek or Latin works were published, numerous professional copies were sometimes made simultaneously by scribes in a scriptorium, each making a single copy from an original that was declaimed aloud.