Auction introduction: The 20th/21st Century: London Evening Sale returns on 9 October, presenting the best of Impressionist, modern, post-war and contemporary art. Aligned with Frieze art fair, a convening moment for collectors in London, the highly anticipated auction will feature important works by some of the most renowned artists of the period. Christie’s is delighted to be offering Jeff Koons’s celebrated sculpture Balloon Monkey (Blue) as one of the highlights of the sale. The sculpture will be installed in St James’s Square from 30 September.