Accountability is key to realising the full potential of the IoT. This is for reasons of adoption and public acceptability, and to ensure that the technologies deployed are, and remain, appropriate and fit for purpose. Though technology generally is subject to increasing legal and regulatory attention, the physical, pervasive and autonomous nature of the IoT raises specific accountability challenges, relating to safety and security, privacy and surveillance, and general questions of governance and responsibility. This article considers the emerging ‘systems of systems’ nature of the IoT, giving the broad legal context for these concerns, to indicate technical directions and opportunities for improving levels of accountability regarding technologies that will increasingly underpin and pervade society.