Undeciphered writing systems are writing systems that experts have not successfully translated or understood in a way that is widely accepted by scholars. Most of these systems are from ancient times, but a few are from the medieval or modern periods. In some cases, there is not enough evidence to determine if the symbols are a true writing system, an early form of writing, or simply non-linguistic symbols. Some modern artistic styles, like asemic writing, look like writing but are intentionally created without clear or stable meaning.

Difficulties in deciphering these systems often include one or more of the following: the lack of texts that use two languages or other clues (such as names or dates that are clearly known); uncertainty about the languages used (which might be completely unique languages); small amounts of written material; and damage or loss of archaeological details that could help test proposed translations. In some cases, it is unclear whether the symbols are even writing at all, as has been debated about the Vinča symbols.

Many attempts have been made to decipher several of these systems, such as the Indus script, the Phaistos Disc, and the Isthmian/Epi-Olmec script. However, these attempts remain controversial and have not gained widespread agreement among scholars unless otherwise stated.

Inclusion criteria

This list includes writing and sign systems that trusted books and articles by experts describe as not yet understood, not completely understood, or unclear in their meaning. Items that people disagree about whether they are real or if they are writing systems are clearly labeled as such.

Proto-writing

Some early writing systems have not been decoded. This is because there isn't enough information and it's unclear which language they belong to. These systems may never be understood.

American scripts

Many Mesoamerican writing systems are not fully understood, but the Classic/Lowland Maya script is the most studied and deciphered. Other regional systems, such as those linked to the Mixteca-Puebla tradition or the pictorial-historical codex traditions that originated from the Teotihuacan tradition (like Aztec and Mixtec hieroglyphs), have been analyzed in different ways. However, these systems are not always recognized as true writing systems by all scholars, with some believing they are more about visual storytelling than language. In recent years, new research has shown that these systems include symbolic elements ("glyphs") combined with pictures. New methods now focus on how pictures contribute to the meaning of the texts, working alongside logograms (symbols representing words) and phonograms (symbols representing sounds). These pictures may represent larger ideas, called semantograms, which are more complex than individual words or sounds. This suggests that Mixteca-Puebla writing is a type of non-linear writing, where meaning is not arranged in a straightforward sequence.

Texts that are not writing systems

A related idea is that of fake writing systems, which look like writing but are not real. These systems cannot be understood because they do not have clear meaning. This includes many types of writing that are made for art and do not carry real messages. One example is the Codex Seraphinianus.

Another related idea is undeciphered cryptograms, which are secret messages written in codes. These are not writing systems themselves but are coded versions of texts written in known systems. Some of these messages are well-known and are included in lists of secret messages.