This thesis outlines the early developmental history of concrete block in America with special attention being placed on the years leading up to the St. Louis Louisiana Purchase Exposition of 1904. In general, the history of concrete block in contemporary building material histories begins with the innovations in block machinery that took place at the turn of the 20th century. However, the history of concrete block begins much earlier than these innovations. Harmon S. Palmer invented the first commercially successful concrete block machine in 1900, but there were many reasons why concrete block became widely used during the first half of the 20th century. The establishments of a domestic Portland cement industry, the innovations in concrete block machinery, and the marketing and promotion of concrete and concrete block at the 1904 St. Louis Louisiana Purchase Exposition, are all major reasons why concrete block began to be widely used in America.