In the strictest definition of illuminated manuscript, only manuscripts with gold or silver, like this miniature of Christ in Majesty from the Aberdeen Bestiary (folio 4v), would be considered illuminated.
An illuminated manuscript is a manuscript in which the text is supplemented by the addition of decoration, such as decorated initials, borders (marginalia) and miniature illustrations. In the most strict definition of the term, an illuminated manuscript only refers to manuscripts decorated with gold or silver, but in both common usage and modern scholarship, the term is now used to refer to any decorated or illustrated manuscript from the Western traditions. Comparable Far Eastern works are always described as painted, as are Mesoamerican works. Islamic manuscripts may be referred to as illuminated, illustrated or painted, though using essentially the same techniques as Western works.
The earliest surviving substantive illuminated manuscripts are from the period AD 400 to 600, initially produced in Italy and the Eastern Roman Empire. The significance of these works lies not only in their inherent art historical value, but in the maintenance of a link of literacy offered by non-illuminated texts as well. Had it not been for the monastic scribes of Late Antiquity, most literature of Greece and Rome would have perished in Europe; as it was, the patterns of textual survivals were shaped by their usefulness to the severely constricted literate group of Christians. Illumination of manuscripts, as a way of aggrandizing ancient documents, aided their preservation and informative value in an era when new ruling classes were no longer literate.
The majority of surviving manuscripts are from the Middle Ages, although many illuminated manuscripts survive from the Renaissance, along with a very limited number from Late Antiquity. The majority of these manuscripts are of a religious nature. However, especially from the 13th century onward, an increasing number of secular texts were illuminated. Most illuminated manuscripts were created as codices, which had superseded scrolls. A very few illuminated manuscript fragments survive on papyrus, which does not last nearly as long as vellum or parchment. Most medieval manuscripts, illuminated or not, were written on parchment (most commonly of calf, sheep, or goat skin), but most manuscripts important enough to illuminate were written on the best quality of parchment, called vellum.
Beginning in the late Middle Ages manuscripts began to be produced on paper. Very early printed books were sometimes produced with spaces left for rubrics and miniatures, or were given illuminated initials, or decorations in the margin, but the introduction of printing rapidly led to the decline of illumination. Illuminated manuscripts continued to be produced in the early 16th century, but in much smaller numbers, mostly for the very wealthy.
Manuscripts are among the most common items to survive from the Middle Ages; many thousands survive. They are also the best surviving specimens of medieval painting, and the best preserved. Indeed, for many areas and time periods, they are the only surviving examples of painting.
The decoration of this page from a French Book of Hours, ca.1400, includes a miniature, initials and borders