Nassau Senior is one of the most significant economists in the classical tradition. This study is based both on his unpublished and published lectures and writings. Part 1 illustrates Senior's outstanding contribution in synthesizing the various developments of Adam Smith's theories that took place during the first part of the 19th century. Part 2 examines Senior's opinions and influence on social and economic policy, in particular his connection with the passing of the Poor Law Amendment Act of 1834.