This book deals with fault tolerance in Field Programmable Gate Arrays (FPGAs). Reliability core concepts are first presented. The types of faults and their masking phenomena are then explained. The most common fault tolerance analysis methods are detailed, as well as hardening techniques aimed at enhancing reliability. An introduction to FPGAs is also given. Then, for reasons that are explained, the focus is on the Mesh of Clusters FPGA architecture whose basic blocks (logic and interconnect) are hardened in different ways and at different granularity levels (from RTL to transistor level)....