Capability Maturity Model Integration (CMMI) is all about improvement, though it may be a tad bit more complicated than that. IT Business Edge editor Lora Bentley did a good job of getting a CMMI overview in an interview with Ralf Kneuper, who has studied CMMI, process models, quality management and project management.
A new book, "CMMI for Services: Guidelines for Superior Service," also explains CMMI at an introductory level. The book includes the complete model itself. In addition, the book's authors refine the model's introductory chapters, provide marginal notes to clarify the nature of particular process areas, show why their practices are valuable, and insert longer sidebars to explain important concepts. Brief essays by people with experience in different application areas further illustrate how the model works in practice and what benefits it offers. The book's first chapter is available in the Knowledge Network.
Once you've got a grasp on the basics of CMMI, you can look at some of the more advanced CMMI resources we have in the Knowledge Network.