Six Sigma

Advantage: Remove variation from your processes & align to customer demands
Disadvantage: It takes some effort.
If you want more information read everything on this site.

Elliot:  I hope you’re not just fishing for info for a term paper.  In addition to Six Sigma (to reduce the variability of the product provided to the customer) you should also look at Lean to remove wasteful aspects of your business processes, and TOC to identify and key in on the true constraints of your system (fixing a non-constraint is not best value for the investment).
Disadvantages – moves power from “fire-fighters” and “bullies” to those who can analyze the system and gather meaningful data.  Makes mgmt uncomfortable because it uncovers many of their bad decisions of the past.  Is hard work – need to understand physical sciences, statistics, math, and be willing to spend the time/effort on often tedious data gathering.