Art Nouveau was the first major break from historicist architecture at the end of the 19th century. The lecture traces how the movement emerged as a reaction against poor craftsmanship, excessive ornamentation, and industrial mass production seen after the Great Exhibition of 1851, and how it sought inspiration from nature, flowing lines, and biomorphic forms. It also introduces the Arts and Crafts Movement led by William Morris, emphasizing “fitness for purpose,” quality, and functional beauty in everyday objects and buildings. Through examples such as Victor Horta’s Tassel House and Hector Guimard’s Paris Metro entrances, the lecture shows how Art Nouveau brought new flexibility in plans, light-filled interiors, and organic ornamentation, laying the foundations for modern architectural thinking.