The following references will provide a very nice overview of the field – from general theory to in-depth case studies:
2) “Jack Welch and the GE Way: Management Insights and Leadership Secrets of the Legendary CEO” by Robert O. Slater, McGraw-Hill 1998.
3) “Six Sigma for Everyone” by George Eckes, John Wiley and Sons 2003.
4) “Six SIGMA Leadership Handbook” by Rath and Strong Staff, John Wiley & Sons 2003.
Although this set of references is not fully comprehensive, it will certainly get you started in the right direction. Best of luck in your Six Sigma journey.