The Internet of Things is underpinned by the global penetration of network-connected smart devices continuously generating extreme amounts of raw data to be processed in a timely manner. Supported by Cloud and Fog/Edge infrastructures-on the one hand, and Big Data processing techniques-on the other, existing approaches, however, primarily adopt a vertical offloading model that is heavily dependent on the underlying network bandwidth. That is, (constrained) network communication remains the main limitation to achieve truly agile IoT data management and processing. This paper aims to bridge this gap by defining Clustered Edge Computing-a new approach to enable rapid data processing at the very edge of the IoT network by clustering edge devices into fully functional decentralized ensembles, capable of workload distribution and balancing to accomplish relatively complex computational tasks. This paper also proposes ECStream Processing that implements Clustered Edge Computing using Stream Processing techniques to enable dynamic in-memory computation close to the data source. By spreading the workload among a cluster of collocated edge devices to process data in parallel, the proposed approach aims to improve performance, thereby supporting agile data management. The experimental results confirm that such a distributed in-memory approach to data processing at the very edge of an IoT network can outperform currently adopted Cloud-enabled architectures, and has the potential to address a wide range of IoT-related data-intensive time-critical scenarios. KEYWORDS cloud computing, clustered edge computing, data agility, edge computing, internet of things, stream processing 1 INTRODUCTION AND MOTIVATION In the last decade, rapid advances in networking technologies and pervasive Internet connectivity guided the development of Information and Communication Technologies (ICT) in distributed, mobile, and embedded directions. On the one hand, supported by continuously growing datacenter infrastructures, virtualization technologies, service-oriented approaches and utility models, Cloud computing has emerged as an effective paradigm, enabling Internet-based, convenient, Quality-of-Service (QoS)-guaranteed access to a shared pool of configurable computing resources. 1 On the other hand, more and more powerful devices, either static or mobile, such as smartphones, single-board computers (eg, Raspberry Pi and Arduino Yun), or smart objects (eg, home appliances, wearables, and vehicles), have been interconnected as ''things'' through the Internet, giving rise to the Internet of Things (IoT) paradigm and corresponding services and applications. There are already tens of billions connected things, which is estimated to reach hundreds of billions in the next 5-10 years. The total amount of data produced by these objects on a daily basis, measured on a scale of Zettabytes (2 70 bytes), requires corresponding technological solutions for their efficient management, usually framed into the context of the Big Data research.