This paper analyses customs automation which is one of the most powerful tools to increase customs efficiency. It focuses in particular on the benefits and implementation costs of automation. It is part of a series of studies that analyse various aspects of trade facilitation and the objective is to contribute to discussions in the WTO Negotiating Group on Trade Facilitation. Based on cost estimations in customsrelated lending projects, the paper finds that the costs for implementing, maintaining and operating automated customs systems are substantial. However, the very great majority of WTO members have already implemented such systems and past experiences show that the financial benefits in many cases have exceeded the costs over time. Among the various lessons learned from successful implementation of automated customs systems, two are particularly worth highlighting. First, automation should not be considered a panacea for trade facilitation; and second, commitment and financial sustainability are prerequisites for successful customs modernisation involving automation.