Philip Anthony Treacy is an Irish haute couture milliner, or hat designer, who has been mostly based in London for his career, and who was described by Vogue magazine as "perhaps the greatest living milliner". In 2000, Treacy became the first milliner in eighty years to be invited to exhibit at the Paris haute couture fashion shows. He has won British Accessory Designer of the Year at the British Fashion Awards five times, and has received public honours in both Britain and Ireland. His designs have been displayed at the Victoria and Albert Museum and the Metropolitan Museum of Art.

Hat-making or millinery is the design, manufacture and sale of hats and other headwear. A person engaged in this trade is called a milliner or hatter.