A method of producing ethylene and, optionally, propylene comprising: a) subjecting a feedstock to steam cracking to produce a first olefin containing stream; b) heating an ethanol containing stream with heat from a steam cracker; c) passing the heated ethanol containing stream over a dehydration catalyst at a temperature between 200 C to 500 C preferably 250 C to 450 C to produce a second olefin containing stream; d) combining the first and second olefin containing streams to give an initial product stream comprising ethylene and optionally propylene; and e) subjecting the initial product stream to purification comprising at least i) water content reduction ii) hydrogen content reduction iii) reduction of content of molecules containing 4 or more carbon atoms and iv) ethane content reduction.