Popular legend has it that Jack Kerouac wrote On the Road in three weeks, typing it almost nonstop in one big coffee-fuelled burst of creative energy on a 120-foot scroll – replacing regular sheets of paper just interrupted his flow – cooped up in a New York City apartment in 1951. At least this is what Kerouac said in 1959 when asked by TV talk-show host Steve Allen about how long it had taken to write it: ‘Three weeks’. ‘How many?’ replied Allen, adding, in disbelief, ‘That's amazing!’ In reality, Kerouac's book had a much longer and bumpier journey, complete with multiple rewrites. And there were always roadblocks slowing down his creative flow – sometimes even to a complete halt – before sputtering off and gradually gaining steam again towards the final destination. And so it is with this book. It has spent many years on the road: from Oxford to Cambridge, Paris, New York, Washington, DC, Geneva and, finally, back to Oxford.

This personal journey has benefitted from the guidance of many companions along the way to whom I am much indebted. At Oxford, Catherine Redgwell supervised the incipient seed of this work as a master's thesis with great care and infectious charm, and set me on my way, in a northeasterly direction, on the X5 bus to Cambridge.

My arrival in Cambridge to complete a PhD thesis – of which this book is an updated and substantially revised version – was generously supported by the Gates Cambridge Trust and Trinity College, for which I am most thankful. To add to my good fortune, I had the great privilege of being supervised by Professor James Crawford, then Whewell Professor of International Law (now judge of the ICJ). James opened up ever-new horizons in characteristically succinct, but deeply profound and meaningful, ways. He is an inspirational figure in many ways and not only in matters of international law. I am deeply grateful for his guidance and generous support.