The challenges that cities face today are diverse and dependent on the region they are located. Inherently cities are complex structures. To improve service delivery in these complex environments the cities are being augmented by “Internet of Things” (IoT) and “Machine to Machine” (M2M) type of technologies that lead to the emergence of extremely complex Cyber-Physical Systems (CPS), often referred to as “Smart Cities”. To support choices for technology deployments in Smart Cities, one has to gain knowledge about the effects and impact of those technologies through testing and experimentation. Hence experimentation environments are required that support the piloting and evaluation of service concepts, technologies and system solutions to the point where the risks associated with introducing these as part of the cities’ infrastructures will be minimised. With this rational, the TRESCIMO (Testbeds for Reliable Smart City Machine to Machine Communication) project deployed a large scale federated experimental testbed across European and South African regions, allowing for experimentation over standardised platforms and with different configurations. Among others, the main requirement for the testbed federation was to cater for the different contextual dimensions for Smart Cities in Europe and South Africa. The testbed is composed of a standards-based M2M platform (openMTC), using standard FIRE SFA-based management tools (FITeagle) and including a variety of sensors and actuators (both virtual and physical). Furthermore, a Smart City Platform attached to openMTC hosts applications for a variety of stakeholders (i.e. experimenters or typical end-users). Aseries of experiments were conducted with the TRESCIMO testbed to validate the plug-and-play approach and Smart City Platform-as-a-Service architecture. This architecture is positioned to provide smart services using heterogeneous devices in different geographical regions incorporating multiple application domains. This chapter elaborates on, and validates the TRESCIMO testbed by presenting the experimental results and experiences from two trials executed in South Africa and Spain.