EIO

Eio or EIO may refer to:
 * Eio (river) in Norway
 * Eio Books, an American publishing house
 * Eio Sakata (1920–2010), Japanese professional Go player
 * Environmental Investment Organisation
 * European Investigation Order
 * Extended interaction oscillator
 * Enhanced Input/Output, an extension interface for printers, see JetDirect § EIO
 * Eiō, one of the eight major titles of professional shogi