The Ephesian School is a Greek Pre-Socratic school of philosophy of the 5th Century B.C., although essentially it refers to the ideas of just one man, Heraclitus (who did not have any direct disciples or successors that we are aware of), a native of Ephesus in the Greek colony of Ionia.
Along with his fellow Ionians of the Milesian School, he looked for a solution to the problem of change, but his view was that the world witnesses constant change, rather than no change at all. The aphorism "everything is in a state of flux", often attributed to Heraclitus, was probably not actually his, but it does give a reasonable summary of his views. The transformation of material from one state into another does not happen by accident, he held, but rather within certain limits and within certain time and according to law or "logos", according to which all things are one. He considered that the basis of all the universe is an ever-living fire (although this is used more as a symbol of change and process, rather than actual fire), so that the world itself consists of a law-like interchange of elements, symbolized by fire.
He also made the apparently logically incoherent claim that opposite things are identical, so that everything is, and is not, at the same time. This he exemplified by the idea that, although the waters in it are always changing, a river stays the same.
