E1

E1, E01, E.I or E-1 may refer to
*Exponential integral, $E\_1(z)=\; int\_1^infty\; frac\{e^\{-tz\{t\},\; \{\; m\; d\}t~$, mathematical function
* E-1, the paygrade of Private E1 in the United States Military
* E1 Corp., a Korean chemical & oil company, member of the LS Group family
* E1 (Jerusalem), a disputed area in Ma'ale Adumim, east of Jerusalem
* E1 mechanism, in organic chemistry
* E-1 (rank), an enlisted rank in the American army
* E1 regulatory sequence for the insulin gene
* E1 Series Shinkansen, a Japanese high-speed train
* E-1 Tracer, an American airborne early warning aircraft
* E1 (Zimbabwe), a road in Zimbabwe
* Bavarian E I, a German steam engines locomotive model
* EMD E1, a diesel locomotive
* European route E01, from Northern Ireland to Spain
* European walking route E1, a long-distance hiking route from Sweden to Italy
* Fokker E.I (or E.1), a German fighter aircraft
* HMS "E1", an E-class submarine of the Royal Navy
* Honda E1, a predecessor of the ASIMO humanoid robot
* Junkers E.I, the Idflieg designation for the 1916 Junkers J1 aircraft
* LB&SCR E1 class, a 1874 British 0-6-0 steam locomotive
* London Buses route E1, a Transport for London contracted bus route
* London E1, the postcode for Whitechapel and Stepney in London
* LVG E.I, a 1915 German two-seat monoplane
* Mazda E engine #E1, a piston engine
* NCC Class E1, a Northern Counties Committee
* NER Class E1, a 1898 class of small 0-6-0T steam locomotive
* Olympus E-1, a digital single-lens reflex camera
* PRR E1, an American
* SP&S Class E-1, a 1934 steam locomotives class
* Standard E-1, a 1917 early American Army fighter aircraft
* USS E-1 (SS-24), a 1917 E-class submarine of the United States Navy
* WLWR Class E1, a Waterford, Limerick and Western Railway Irish steam locomotive

and also :
* E-carrier level 1, a European telecommunications standard for 2 Mbit/s
* E01 : Iodine-deficiency-related thyroid disorders and allied conditions code
* first part of the pyruvate dehydrogenase enzyme complex