Linear A is one of two currently undeciphered writing systems used in ancient Crete prior to its Mycenaean descendent Linear B. Cretan hieroglyphic is the other. In Minoan times, Linear A was the primary script used in palace and religious writings. It was discovered by archaeologist Arthur Evans.
In the 1950s, Linear B was largely deciphered. Although the two systems share many symbols, this did not lead to a subsequent decipherment of Linear A. Using the values associated with Linear B in Linear A produces unintelligible words. If it uses the same or similar syllabic values as Linear B, then its underlying language appears unrelated to any known language. This has been dubbed Eteocretan language.
Read more about Linear A: The Script, Corpus, Chronology, Discovery, Theories of Decipherment