World's Tallest Dog - Meet The Record Breakers - Guinness World Records - Must Watch Video

The tallest dog is 'Zeus' (USA) a Great Dane, who measured 1.118 m (44 in) tall on 4 October 2011 and is owned by Denise Doorlag and her family, of Otsego, Michigan, USA.

Zeus also took over the 'Tallest dog ever' title from previous holder 'Giant George'.
UPDATE 12/09/2014: Sadly, Zeus passed away this week at the age of five. "He will be greatly missed by his lovely owners and will live on in Guinness World Records history as the Tallest Dog we ever measured.” said GWR picture editor, Michael Witty.