In 1970 the first Netherlands Yearbook of International Law (NYIL) was published. The current Volume is No. 50, which means that the Yearbook has now been with us for half a century. The current General Editors decided not to let this moment pass unnoticed, and have devoted this entire Volume to an analysis of the phenomenon of Yearbooks in international law as such. Indeed, not many academic disciplines have Yearbooks, so why do we? What is the added value of having a Yearbook alongside the abundance of international law journals, regular monographs and edited volumes that are produced each year? Does the existence of Yearbooks tell us something about who we are, or who we think we are, or what we have to contribute to the world?