What is an avenue? When and why did avenues emerge in the landscape? When and how did avenues become urban routes? Which physical features related early seventeenth century avenues to their nineteenth century descendants? The research involved in this book set out to answer these questions. The existing literature regarding avenues was either too general, neglecting a thorough examination of case studies, or too particular, focusing on individual traits. In this book, the focus is shifted from individual cases to urban type; nevertheless, conclusions are grounded on the detailed comparative analysis of three case studies to avoid generalist preconceptions. The three case studies chosen were the Avenue des Champs-Élysées, Regent Street, and Avenida da Liberdade. The detailed account of why and how the three chosen case studies were commissioned, conceived and built provides an illustrated sequence of how the avenue, as an urban type, was used in the seventeenth, nineteenth and twentieth centuries. This sequence challenges two fundamental ideas. Firstly, as may have been guessed by those who have walked through Regent Street, it challenges the understanding of an avenue as a tree-lined pathway, replacing it by a broader definition of the avenue as a public space conceived to physically merge landscape and city. Secondly, instead of reducing the avenue to a type created by enlightened absolute power, as is too often suggested, this book presents the nineteenth-century avenue as a type emerging from a society moved by economic and political liberalism. In the end, the avenue is depicted as one more tool in the modern path, designed to address societal challenges by merging progressive reasoning with memories of a past, which must be remembered but never relived.