So good old Humphrey back in 1989 wrote The Bible on managing the software process and its still being used today. This is one of those classics as far as software engineering goes. It is amazingly small book and yet packs more information in it than can be imagined. Not light reading -- 2 chapters were excruciatingly difficult to read. That being said I'm glad I read it.
The book is, as someone put it, a precursor to the CMM model of the early 2000s. A fascinating book with core principles still valid. Just not sure how old technologies fit in. But barring that, this book will hold at least until some radically different method of developing software comes up. Boring in some parts (it is a techie book), but one can just glaze over those pages and move on.
Really the definitive book on the Capability Maturity Model for Software. One can pick up the model elsewhere, but this is the place to get the understanding of the model.