Cabinets of curiosities (German: Kunstkammer [ˈkʊnstˌkamɐ] and Kunstkabinett [ˈkʊnstkabiˌnɛt]), also known as wonder-rooms (German: Wunderkammer [ˈvʊndɐˌkamɐ] ^ⓘ), were encyclopedic collections of objects whose categorical boundaries were, in Renaissance Europe, yet to be defined. Although more rudimentary collections had preceded them, the classic cabinets of curiosities emerged in the sixteenth century. The term cabinet originally described a room rather than a piece of furniture. Modern terminology would categorize the objects included as belonging to natural history (sometimes faked), geology, ethnography, archaeology, religious or historical relics, works of art (including cabinet paintings), and antiquities. In addition to the most famous and best documented cabinets of rulers and aristocrats, members of the merchant class and early practitioners of science in Europe formed collections that were precursors to museums.

Cabinets of curiosities served not only as collections to reflect the particular interests of their curators but also as social devices to establish and uphold rank in society. There are said to be two main types of cabinets. As R. J. W. Evans notes, there could be "the princely cabinet, serving a largely representational function, and dominated by aesthetic concerns and a marked predilection for the exotic," or the less grandiose, "the more modest collection of the humanist scholar or virtuoso, which served more practical and scientific purposes." Evans goes on to explain that "no clear distinction existed between the two categories: all collecting was marked by curiosity, shading into credulity, and by some sort of universal underlying design".

In addition to cabinets of curiosity serving as an establisher of socioeconomic status for its curator, these cabinets served as entertainment, as particularly illustrated by the proceedings of the Royal Society, whose early meetings were often a sort of open floor to any Fellow to exhibit the findings his curiosities led him to. However purely educational or investigative these exhibitions may sound, the Fellows in this period supported the idea of "learned entertainment," or the alignment of learning with entertainment. This was not unusual, as the Royal Society had an earlier history of a love of the marvellous. This love was often exploited by eighteenth-century natural philosophers to secure the attention of their audience during their exhibitions.

The earliest pictorial record of a natural history cabinet is the engraving in Ferrante Imperato's Dell'Historia Naturale (Naples 1599) (illustration). It serves to authenticate its author's credibility as a source of natural history information, by showing his open bookcases (at the right), in which many volumes are stored lying down and stacked, in the medieval fashion, or with their spines upward, to protect the pages from dust. Some of the volumes doubtless represent his herbarium. Every surface of the vaulted ceiling is occupied with preserved fishes, stuffed mammals and curious shells, with a stuffed crocodile suspended in the centre. Examples of corals stand on the bookcases. At the left, the room is fitted out like a studiolo with a range of built-in cabinets whose fronts can be unlocked and let down to reveal intricately fitted nests of pigeonholes forming architectural units, filled with small mineral specimens. Above them, stuffed birds stand against panels inlaid with square polished stone samples, doubtless marbles and jaspers or fitted with pigeonhole compartments for specimens. Below them, a range of cupboards contain specimen boxes and covered jars.

In 1587 Gabriel Kaltemarckt advised Christian I of Saxony that three types of items were indispensable in forming a "Kunstkammer" or art collection: firstly sculptures and paintings; secondly "curious items from home or abroad"; and thirdly "antlers, horns, claws, feathers and other things belonging to strange and curious animals". When Albrecht Dürer visited the Netherlands in 1521, apart from artworks he sent back to Nuremberg various animal horns, a piece of coral, some large fish fins and a wooden weapon from the East Indies.

The highly characteristic range of interests represented in Frans II Francken's painting of 1636 (illustration, above) shows paintings on the wall that range from landscapes, including a moonlit scene—a genre in itself—to a portrait and a religious picture (the Adoration of the Magi) intermixed with preserved tropical marine fish and a string of carved beads, most likely amber, which is both precious and a natural curiosity. Sculptures both classical and secular (the sacrificing Libera, a Roman fertility goddess) on the one hand and modern and religious (Christ at the Column) are represented, while on the table are ranged, among the exotic shells (including some tropical ones and a shark's tooth): portrait miniatures, gem-stones mounted with pearls in a curious quatrefoil box, a set of sepia chiaroscuro woodcuts or drawings, and a small still-life painting leaning against a flower-piece, coins and medals—presumably Greek and Roman—and Roman terracotta oil-lamps, a Chinese-style brass lock, curious flasks, and a blue-and-white Ming porcelain bowl.

The Kunstkammer of Rudolf II, Holy Roman Emperor (ruled 1576–1612), housed in the Hradschin at Prague, was unrivalled north of the Alps; it provided solace and retreat for contemplation that also served to demonstrate his imperial magnificence and power in the symbolic arrangement of their display, ceremoniously presented to visiting diplomats and magnates.

Rudolf's uncle, Ferdinand II, Archduke of Austria, also had a collection, organized by his treasurer, Leopold Heyperger, which put special emphasis on paintings of people with interesting deformities, which remains largely intact as the Chamber of Art and Curiosities at Ambras Castle in Austria. "The Kunstkammer was regarded as a microcosm or theater of the world, and a memory theater. The Kunstkammer conveyed symbolically the patron's control of the world through its indoor, microscopic reproduction." Of Charles I of England's collection, Peter Thomas states succinctly, "The Kunstkabinett itself was a form of propaganda."