E21

E21 may refer to:
 * BMW E21, an automobile platform
 * HMS E21
 * European route E21
 * DRG series E 21, different locomotives of the German National Railroad
 * E21 - Code that it designates the Astronomical observatory of Norm Roses, Leyburn
 * E21 - code ECHO of the Nimzo-Indian Defence, opening of chess
 * Eyeshield 21, a manga based on American Football
 * Economics21, or e21, web portal of the Manhattan Institute for Policy Research
 * Kajang–Seremban Highway, route E21 in Malaysia
 * The Lotus E21, a Formula One racing car