There were in fact two main stages in the development of the Cretan script: pictographic and syllabic. The pictograms (or hieroglyphs) were used in the Middle Minoan period of the history of Crete (2100 - 1700 BC) and are divided into two variants - Early, used mainly on seals, and Late, which is met in inscriptions on tablets. About 150 pictographic inscriptions were found at all, they depict people, animals, plants, and written from either from the right or from the left.
Pictograms can hardly be deciphered, it is supposed to have denote not only words but also symbols and determinatives. Some signs could sound as syllables. This script's origin can be traced in Egypt, because the shape of pictograms sometimes reminds Egyptian hieroglyphic.
The Linear A script appeared in the Middle Minoan period (1700 - 1550 BC). It was a syllable one, used a limited number of symbols and therefore are easier to study. The script, found on seals, instruments, tablets on the islands of Crete, Phera and Melos, includes from 77 to 100 symbols, each of them denoting a syllable. The language of them is still unknown, but it is for sure non-Indo-European, and can be referred to as one of the "Mediterranean" languages. This language did not make any distinction between long and short vowels, voiced and voiceless consonants, l and r.
The Linear A script was a basis for the development of the Linear B writing, which emerged here on Crete in about 1450 BC and soon spread to continental Greece, where in Pylos and Mycenae large archives of Linear B documents were excavated. The Linear B, the first script accepted by Indo-Europeans, became a part of the Mycenaean culture, the first civilization of continental Europe. It was written both in Greek (more exactly, its archaic Mycenaean dialect), and in aboriginal languages of Crete and other Aegean islands. The Linear B script contained 88 syllabic letters and several determinative symbols (logograms).
Since it was borrowed from non-Indo-Europeans, Linear B was not convenient for the Greek language, it did not reflect many important phonetic features of the tongue, and could not, for example, end a word in -s or any other consonant. Still, the script was in wide use in Greek city states (Pylos, Tyrinth, Mycenae), and a great lot of economic documents were written in it. After 1200 BC, when Doric tribes from the North invaded Greece, the Mycenaean civilization fell, and its advances were forgotten by the people. It is interesting, that Greeks kept a sort of unpleasant feeling about the old script, maybe because it was psychological associated with cruel royal scribes and tax collectors. Five centuries later, Greeks developed their own alphabet.
Languages which used the script:
Hellenic (Mycenaean Greek), non-Indo-European (Eteocretan).