Managing the Software Process
ISBN 0201180952 WattsHumphrey - New York: Addison-Wesley, 1989 - From the preface: "This book describes the technical and managerial topics these (software process) assessments have found most critical for improvement."
If I'm not mistaken, what this book describes as the "Software Process Maturity Framework" would later become formalized as the CapabilityMaturityModel. -- AnthonPang
For a brief history of CMM, see http://www.sei.cmu.edu/publications/documents/93.reports/93.tr.024.html
Also, for what I believe is the origin of CMM, see the "QualityManagementMaturityGrid" (chapter 3, pp.33-33) of "QualityIsFree" by Philip Crosby, published in 1979. This book is also referenced in "References" section of the CMM document. The five stages: Uncertainty, Awakening, Enlightenment, Wisdom, and Certainty.
This book was my favourite for a couple of months until I read Fowler's RefactoringBook, which lead me to read ExtremeProgrammingExplained. Now I only keep this book for historical value.
For Humphrey's newer thoughts on improving software, see PersonalSoftwareProcess and TeamSoftwareProcess.