Soft errors are becoming an increasingly important issue for circuit reliability. Traditional techniques to protect against soft errors, like triple modular redundancy (TMR), have a large cost in terms of area and power. This has motivated the development of specific protection techniques for various types of circuits. In this paper, techniques to protect adaptive filters are presented, which provide reasonable reliability with reduced cost and power consumption. An adaptive equalizer case study is used to discuss and evaluate the proposed techniques in terms of both protection and cost.