Program assurance is a systematic approach to measure the likelihood of success of a program and proposing improvements that will ensure success.
It is used for:
Program assurance also:
For large programs assurance is generally independent. It may be undertaken by an external body or an internal department that reports independently from the program manager. In both cases it generally provides an independent view of the program status to the program board or executive. For smaller programs program assurance may be undertaken from within the program or report into a portfolio office. 
The key difference between program assurance and program quality management or audit, is that program assurance tends to look at the potential impact of the program's approach. 
Assurance may either focus on program delivery, program solutions or both may have equal weight. Within major IT programs external assurance often focuses on program delivery and would concentrate on program plans and capability. Where assurance also covers the solution this would include the business processes, systems, infrastructure, service and hosting. Solution may also cover the approach to design, delivery and implementation.
Program assurance tends to cover three separate styles of assurance: Continuous assurance throughout the life of the program; Point reviews or periodic reviews; focused reviews that concentrate on a particular aspect of a program. For very large programs all three would be undertaken with continuous assurance reporting to the program board on a regular basis, and point or focused reviews being undertaken at strategic points. 
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