Fault tolerance is the ability of a system to perform its function correctly even in the presence of internal faults. We should accept that, relying on software techniques for obtaining dependability means accepting some overhead in terms of increased size of code and reduced performance (or slower execution). N-version programming achieves redundancy through the use of multiple versions. Failures are detected by comparing the results of the different versions. In this paper we will discuss the techniques of software fault tolerance such as recovery blocks, N-version programming, single version programming, multi-version programming, Comparison of N-Version with recovery block .