Lucy Douglas Cochrane (February 19, 1920 - November 8, 2003), better known as C Z Guest, was an American socialite who achieved a degree of fame as a fashion icon. Her unfussy, clean-cut style was seen as typically American.

She was born in Boston and her father, Alexander Lynde Cochrane, was an investment banker. She acquired the nickname "C Z" from her younger brother.

In 1947, she became the second wife of Winston Frederick Churchill Guest (1906-1982), a polo player, grandson of Henry Phipps , and a great-grandson of the seventh Duke of Marlborough. Ernest Hemingway was best man at the wedding, which took place in Havana. The couple had two children, Alexander and Cornelia ; Cornelia was named the 1980s "Deb of the Decade".

Guest was probably best known for the column she wrote on gardening for the New York Post. Her first book about gardening (entitled, appropriately enough, First Garden) was illustrated by her friend Cecil Beaton. Other friends included Truman Capote and the Duke and Duchess of Windsor.

She died aged 83 at her Long Island home.