WORDS is the main international event in Combinatorics on Words. It is a biannual conference devoted to research of words (i.e., finite or infinite sequences of symbols over a finite alphabet) from combinatorial, algebraic and algorithmic points of view. The emphasis of the conference is on mathematical theory of words but the conference is also open to applications, mainly in computer science, biology, linguistics and physics, gaining from the fact that words arise as a natural object in many areas. The eighth edition of the conference was organized in Prague from 12th to 16th September 2011 as a joint undertaking of the Czech Technical University and the Charles University. This volume consists of contributed papers accepted for presentation at the conference and summaries of invited lectures.