This book is the first major study to analyse the word 'dialogue' in the documents of the Second Vatican Council. 'Dialogue' actually translates two different Latin words, colloquium and dialogus, which do not mean the same thing. After a clear explanation of the important distinction between the dialectic of Thomism, where dialogue leads to an end-point, and the modern meaning of dialogue as an open-ended process between equal partners, the book argues that these dissimilar concepts became blurred in the documents of the Council. A careful analysis of the interpretation of this word in a comparison across five major English translations of the documents demonstrates how