Abstract. These three symbols represent to a modern mathematician three Dynkin diagrams, but in a sense they have been known to mathematicians for hundreds of years. When the Greeks classified the regular solids, they were really showing they knew about E6, E7 and E8 and when the 19th century geometers got excited about the 27 lines on a cubic surface or the 28 bitangents to a quartic curve they were really studying E6 and E7 in their own terms. Today string theorists search for a theory of the universe by looking at E8 X E8. The talk will aim to show how E6, E7 and E8 lie at the heart of some very concrete mathematics.