The mall was originally developed by investments from the Korea International Trade Association. COEX Mall was designed by the US interior design company RTKL. COEX Mall was also designed by Gensler, under the theme "Unfolding Sky", emphasizing seamless flow and openness. Construction of the mall began on May, 1997 and finished in April, 2000. Construction costs amounted to ₩140 billion (US$150 million).[1]