This chapter provides a survey of state-of-the art design strategies to handle faults with special stress on redundancy-based techniques. Section one presents an overview of fault avoidance design strategies. Section two provides a survey of fault tolerance techniques. The notion of redundancy and its different types are presented and a notation, which may be used to describe the different types of redundancy, is introduced. The concepts, capabilities and applications of the different techniques based on structural (SR), information (IR) and time redundancy (TR) are compared and discussed.