Rongorongo (/ˈrɒŋɡoʊˈrɒŋɡoʊ/ or /ˈrɒŋoʊˈrɒŋoʊ/; Rapa Nui: roŋoroŋo [ˈɾoŋoˈɾoŋo]) is a system of glyphs discovered in the 19th century on Easter Island that has the appearance of writing or proto-writing. Numerous attempts at decipherment have been made, but none have been successful. Although some calendrical and what might prove to be genealogical information has been identified, none of the glyphs can actually be read. If rongorongo does prove to be writing and to be an independent invention, it would be one of very few inventions of writing in human history.

Two dozen wooden objects bearing rongorongo inscriptions, some heavily weathered, burned, or otherwise damaged, were collected in the late 19th century and are now scattered in museums and private collections. None remain on Easter Island. The objects are mostly tablets shaped from irregular pieces of wood, sometimes driftwood, but include a chieftain's staff, a tangata manu statuette, and two reimiro ornaments. There are also a few petroglyphs which may include short rongorongo inscriptions. Oral history suggests that only a small elite was ever literate and that the tablets were sacred.

Authentic rongorongo texts are written in alternating directions, a system called reverse boustrophedon. In a third of the tablets, the lines of text are inscribed in shallow fluting carved into the wood. The glyphs themselves are outlines of human, animal, plant, artifact and geometric forms. Many of the human and animal figures, such as glyphs 200 and 280 , have characteristic protuberances on each side of the head, possibly representing eyes.

Individual texts are conventionally known by a single uppercase letter and a name, such as Tablet C, the Mamari Tablet. The (somewhat variable) names may be descriptive or indicate where the object is kept, as in the Oar, the Snuffbox, the Small Santiago Tablet, and the Santiago Staff.

Rongorongo is the modern name for the inscriptions. In the Rapa Nui language, roŋoroŋo or rogorogo means "to recite, to declaim, to chant out".

The original name—or perhaps description—of the script is said to have been kōhau motu mo roŋoroŋo, "lines incised for chanting out", shortened to kōhau roŋoroŋo or "lines [for] chanting out". There are also said to have been more specific names for the texts based on their topic. For example, the kōhau taꞌu ("lines of years") were annals, the kōhau ika ("lines of fishes") were lists of persons killed in war (ika "fish" was homophonous with or used figuratively for "war casualty"), and the kōhau raŋa "lines of fugitives" were lists of war refugees.

Some authors have understood the taꞌu in kōhau taꞌu to refer to a separate form of writing distinct from roŋoroŋo. Barthel recorded that "The Islanders had another writing (the so-called 'taꞌu script') which recorded their annals and other secular matters, but this has disappeared." But Steven Roger Fischer writes that "the taꞌu was originally a type of roŋoroŋo inscription. In the 1880s, a group of elders invented a derivative 'script' [also] called taꞌu with which to decorate carvings in order to increase their trading value. It is a primitive imitation of roŋoroŋo." An alleged third script, the mama or vaꞌevaꞌe described in some mid-20th-century publications, was "an early twentieth-century geometric [decorative] invention".

The forms of the glyphs are standardized contours of living organisms and geometric designs about one centimeter high. The wooden tablets are irregular in shape and, in many instances, fluted (tablets B, E, G, H, O, Q, and possibly T), with the glyphs carved in shallow channels running the length of the tablets, as can be seen in the image of tablet G at right. It is thought that irregular and often blemished pieces of wood were used in their entirety rather than squared off due to the scarcity of wood on the island.