Software fault tolerance & reliability, as a property of dependability is on the most important non-functional characteristic of software intensive systems. This is especially true  for  specific  domains,  like  embedded  systems,  service-oriented  systems  and  so  on. Despite all activities denoted to make high-quality & bug-free software systems, much has been written about why software is so defect prone and about why the problem of designing and writing software is so intrinsically difficult. Researchers recognize both the essential and accidental difficulties of producing correct software. Essential difficulties arise from the inherent challenge of understanding a complex application and operating environment, and from having to construct a structure comprising an extremely large number of states, with very complex state-transition rules. Further, software is subject to frequent modifications, as new features are added to adapt to changing application needs. In addition, as hardware and operating system platforms change with time, the software has to adjust appropriately. Finally, software is often used to paper over incompatibilities between interacting system components. Considering all these aspect of software system designing, it is necessary to learn about introductory and advanced techniques to make software more and more fault tolerant and reliable.