This paper presents the Flexible Radio Kernel (FRK), a configuration and execution management environment for hybrid hardware/software flexible radio platforms. The aim of FRK is to manage platform reconfiguration for multi-mode, multi-standard operation, with different levels of abstraction. A high level framework is defined and described. Its goal is to manage multiple Medium Access Control layers and to enable cooperation algorithms for cognitive radio. A low-level environment is also available to manage platform reconfiguration for radio operations. Radios can make use of hardware or software elements, and configuration state is hidden to the high-level layers, offering pseudo concurrency (time sharing) properties independently of the nature of the elements implementation. This study presents a global view of FRK, with a specific focus on its software architecture and its support of configurable hardware. The effectiveness of the approach is demonstrated through a practical example.