Undeciphered writing systems

Many undeciphered writing systems exist today; most date back several thousand years, although some more modern examples do exist. The term "writing systems" is used here loosely to refer to groups of glyphs which appear to have representational symbolic meaning, but which may include "systems" that are largely artistic in nature and are thus not examples of actual writing.

The difficulty in deciphering these systems can arise from a lack of known language descendants or from the languages being entirely isolated, from insufficient examples of text having been found and even (such as in the case of Vinča) from the question of whether the symbols actually constitute a writing system at all. Some researchers have claimed to be able to decipher certain writing systems, such as those of Epi-Olmec, Phaistos and Indus texts; but to date, these claims have not been widely accepted within the scientific community, or confirmed by independent researchers, for the writing systems listed here (unless otherwise specified).

Proto-writing
Certain forms of proto-writing remain undeciphered and, because of a lack of evidence and linguistic descendants, it is quite likely that they will never be deciphered.

Yellow River civilization

 * Jiahu symbols – Peiligang culture, from China, c. 6600 - 6200 BC.
 * Damaidi symbols – Damaidi, from China, earliest estimated dates range from the Paleolithic to approximately 3000 years ago.
 * Dadiwan symbols – Dadiwan, from China, c. 5800 - 5400 BC.
 * Banpo symbols – Yangshao culture, from China, 5th millennium BC.
 * Jiangzhai symbols – Yangshao culture, from China, 4th millennium BC.
 * Dawenkou symbols – Dawenkou culture, c. 2800 - 2500 BC.
 * Longshan symbols – Longshan culture, from China, c. 2500 - 1900 BC.

Yangtze civilization
Other areas
 * Wucheng symbols – Wucheng culture, from China, c. 1600 BC.
 * Sawveh – Guangxi, from China; possible proto-writing or writing.

Neolithic signs in Europe

 * Dispilio Tablet – Neolithic Europe, from Greece, c. 5202 BC.
 * Vinča symbols – Neolithic Europe, from Central Europe and Southeastern Europe, c. 4500 BC - 4000 BC.

South Asia

 * Indus script, c. 3500 BC to 1900 BC.
 * Vikramkhol inscription, c. 1500 BC.
 * Megalithic graffiti symbols, c. 1000 BC - 300 AD, possible writing system and possible descendant of Indus script.
 * Pushkarasari script – Gandhara, 3rd century BC to 8th century AD.
 * Shankhalipi, c. 4th to 8th century.

West Asia

 * Proto-Elamite script, c. 3200 BC.
 * Jiroft script, c. 2200 BC.
 * Byblos syllabary – the city of Byblos, c. 1700 BC.
 * Cypro-Minoan syllabary, c. 1550 BC.

East Asia

 * Ba–Shu scripts, 5th to 4th century BC.
 * Khitan large script and Khitan small script – Khitan, 10th century, not fully deciphered.
 * Tujia script.

Southeast Asia

 * Singapore Stone, a fragment of a sandstone slab inscribed with an ancient Southeast Asian script, perhaps Old Javanese or Sanskrit. At least 13th century, and possibly as early as 10th to 11th century.

Central Asia

 * Oxus script, c. 2200 BC.
 * Issyk inscription, Kazakhstan, c. 4th century BC.
 * Kushan script, c. 2nd century BC - 7th century AD, partially deciphered.

Europe

 * Cretan hieroglyphs, c. 2100 BC.
 * Linear A and Cretan hieroglyphs are scripts from an unknown language, one possibility being a yet to be deciphered Minoan language. Several words have been decoded from the scripts, but no definite conclusions on the meanings of the words have been made.
 * Phaistos Disc, c. 2000 BC.
 * Linear A, c. 1800 BC - 1450 BC, partially deciphered. Phonetic transcriptions can be read with some approximation. Scholars can understand some of the words, and get a general idea of the document's contents.
 * Grakliani Hill script – Grakliani Hill, c. 11th - 10th century BC.
 * Paleohispanic scripts.
 * Southwest Paleohispanic script, from c. 700 BC.
 * Sitovo inscription, c. 300 - 100 BC.
 * Alekanovo inscription, c. 10th - 11th century.
 * Rohonc Codex, c. 1600s - 1800s.
 * Folio 7r-v of British Library manuscript MS 73525, pre-1550, possibly liturgical.
 * Voynich manuscript, carbon dated to the 15th century.
 * Some scholars consider the corpus of Pictish symbol stones to be an undeciphered writing system.
 * An inscription in the Pisa Baptistery.

North Africa

 * The Starving of Saqqara - possibly dating to pre-dynastic Egypt.

Sub-Saharan Africa

 * Eghap script – Cameroon, c. 1900, partially deciphered.
 * Ancient inscriptions in Somalia - According to the Ministry of Information and National Guidance of Somalia, inscriptions can be found on various old Taalo Tiiriyaad structures. These are enormous stone mounds found especially in northeastern Somalia. Among the main sites where these Taalo are located are Xabaalo Ambiyad in Alula District, Baar Madhere in Beledweyne District, and Harti Yimid in Las Anod District.

Andean Region

 * Quipu – Inka Empire and predecessor states, like the Wari Empire or the Caral-Supe Civilization, c. 2600 BC - 20th century, with linguistic usage of it lasting up to the end of the 18th century. It was used, among other peoples, by Quechua speakers (who called it "Khipu"), Aymara speakers ("Chinu") and Mapuche speakers ("Püron"). It could possibly be a writing system or a set of writing systems, since three Quechua words have been recently deciphered: one in 2005 and the other two in 2017. These decipherments apparently show that linguistic usage of Quipus followed a logosyllabic pattern.

Mesoamerica

 * Olmec Hieroglyphs, c. 900 BC - 500 BC, possibly the oldest Mesoamerican script.
 * Zapotec Hieroglyphs, c. 500 BC - 800 AD, possibly logosyllabic.
 * Isthmian Hieroglyphs, c. 500 BC - 500 AD, apparently logosyllabic.
 * Izapan Hieroglyphs, Late Preclassic, possibly logosyllabic. Guatemalan and Chiapas Pacific Coast. Probably an offshoot of Epi-olmec.
 * Ñuiñe Hieroglyphs, c. 400 AD - 800 AD. Similar to Zapotec and possibly an offshoot of it in the Mixteca Baja. Possibly logosyllabic.
 * Teotihuacan Hieroglyphs, c. 100 BC - 700 AD, possibly a logosyllabary. Possibly inspired from the Zapotec script, and itself being the probable ancestor of the Postclassic Mixteca-Puebla Script.
 * Cotzumalhuapa Hieroglyphs, 0 CE - 1000 CE. A script in the Lower Pacific Coast which presents influences of Teotihuacan and the Maya Lowlands. Probably a logosyllabary.
 * Epiclassic Hieroglyphic Scripts of El Tajín, Xochicalco, Cacaxtla and Teotenango. Probably logosyllabic. Descended from Teotihuacan Hieroglyphs
 * Early Postclassic Hieroglyphic Scripts of Tula and Chichén Itzá. Probably logosyllabic. Descended from the Epiclassic Hieroglyphic Scripts. Mother script of Mixteca-Puebla Hieroglyphs.

Virtually all Mesoamerican Glyphic Scripts remain undeciphered, with the only exceptions being Lowland Maya Hieroglyphs and Mixteca-Puebla Hieroglyphs (represented by several regional glyphic traditions used in the whole of Postclassic Mesoamerica outside the Maya Lowlands, the most well known of which are the Aztec Script and the Mixtec Script).

Oceanian scripts

 * Rongorongo – Rapa Nui. After 900, before 1860. Probably logosyllabic.

Related concepts: texts that are not writing systems
One very similar concept is that of false writing systems, which appear to be writing but are not. False writing cannot be deciphered because it has no semantic meaning. These particularly include asemic writing created for artistic purposes. One prominent example is the Codex Seraphinianus.

Another similar concept is that of undeciphered cryptograms, or cipher messages. These are not writing systems per se, but a disguised form of another text. Of course any cryptogram is intended to be undecipherable by anyone except the intended recipient so vast numbers of these exist, but a few examples have become famous and are listed in list of ciphertexts.