This workshop explores how we see customary international law and its evolution in today’s uncertain and increasingly secretive times. It first considers two contemporary frameworks for the consideration of custom and what these tell us about our understanding of international law today, and then focuses on custom’s traditional elements; practice and opinio juris sive necessitatis. Practice is only relevant if it is ‘for the purposes of the law’, which is to say that what constitutes relevant practice is governed by the law. What then are the law’s conditions today in this regard? The second element of custom, opinio juris, has long been controversial. The perennial question can still be asked: is opinio juris relevant today? Assuming it is, how might custom’s subjective element be affected depending on the nature of the asserted practice (obligation, prohibition, or permission)? And crucially, in today’s fast paced digital world, how do temporal factors impact custom’s subjective element, which is also to ask, what can we say now of the idea of instant custom?