In 1909, Arnold van Gennep wrote a book on the rites of passage where he discussed what he called the liminal phase (from Lat. limes, border, pl. limites) through which boys in a number of cultures had to pass in order to become men. With his Dutch name, his German birth, his move to France with his divorced mother at the ripe age of six, and his interest in the Arab world, he was nothing if not a man in transition between different life worlds. His scholarly life, too, was a life of transit; from haute école to haute école, from France to Switzerland. To top it all, when the institutionalisation of the social sciences in France was finally hitting its stride with the emergence of Durkheim's année-school, van Gennep was marginalised. There was no closure to his scholarly travels. Van Gennep remained liminal, remained in becoming. In his own terms, his rite de passage never ended. He went from pre-liminality to liminality – a condition that his greatest follower, the symbolic interactionalist anthropologist Victor Turner characterised as existing betwixt and between socially recognised positions – without entering the post-liminal phase of having been fully incorporated into one of those already existing positions. Van Gennep made it his life to deal with the uncertainties and the danger that any social order ascribes to those who are between categories. With this Forum, liminality arrives within the discipline of International Relations (IR) in earnest. The rest of this Introduction will give some historical background that situates the Forum's three post-structural protagonists, note how their undertaking is part of a wider thrust towards process-oriented and relation-oriented work within the social sciences and introduce the pieces.