Abstract. Monitoring systems are nowadays ubiquitous in complex environments, such as Grids. Their use is fundamental for performance evaluation, problem spotting, advanced debugging and per-use accounting. Building such systems raises challenging issues, like data gathering from Grid components, low intrusiveness, ease of use, adaptive data visualization, fault-tolerance and self-maintenance. This paper presents a new layered architecture, named Toytle, specifically designed to address these issues in the context of control Grids. All their components, from computing and network resources to complete physical processes with soft time constraints, can be monitored with Toytle. The architecture’s layers, namely the distributed core, the hierarchical connections and the local monitors, have been designed to ensure scalability, highspeed sampling and efficient dealing with large data bursts. The future Toytle implementation will adapt existing tools and also create entirely new modules...