For many decades, governments have successfully intercepted telecommunications to collect information about—potential—criminals and terrorists. A crucial part of contemporary policy is legislation that requires telecommunications providers to make their networks and services interceptable. This paper discusses two examples of interceptability legislation: the Communications Assistance for Law Enforcement Act (CALEA) in the US and the Telecommunications Act in the Netherlands, in order to focus on basic questions, considerations, and trade-offs relevant to designing legal interceptability laws. In particular, the sustainability of interceptability policies as laid down in these laws is questioned, since they are under significant pressure. Technical and market developments challenge their effectiveness and costs. These developments include IP-based services, seamless roaming, default encryption at various telecommunications layers, and the ‘identity boom’. Market challenges include substantial shifts in the value chain and the explosion of traffic volumes. This paper aims to determine which interceptability policy is best suited for coping with the challenges that lie ahead.