My most recent completed book was The Doula Book by Marshall H. Klaus, John H. Kennel, and Phyllis H. Klaus. (Did anyone else notice that all the authors have the same middle initial?)
It's a slim, reader-friendly book, weighing in at just about 190 pages, plus some helpful appendices. The writing style is a bit clinical but accessible.
This book makes a strong case for doulas, and it does so in large part by presenting a wealth of data. If you want to cite a figure for the concrete good that doulas do, this is the book for it. They bring together an impressive amount of studies and make a compelling case for doulas decreasing the need for pain medication, medical intervention, and Cesarean sections, not to mention increasing satisfaction with the birth experience, and even helping to improve mother-baby bonding so much that it leads to a decrease in child abandonment and abuse! Wow!
The book also explains what a doula is in quite some detail, and really goes into the details of exactly what a doula does. That seems like it's sure to be very helpful to someone who's curious but really has no clue about doulas. All the talk of techniques that doulas use was very interesting to me, too, as I'm looking into becoming a doula.
They have a special chapter for talking about the role of the father in birthing. First of all, the language of this book isn't very inclusive - as it always seems to assume that there is a partner in the picture, and that that partner is male. (They give a nod to this book being for all kinds of families somewhere early on, but it's all about "mother and father" from that point on. Admittedly, most families will fit that description, but just a heads-up to others.) Anyway, I thought that this book was sort of discouraging about how much a father can really do for the birthing mother in labor. On the other hand, it was a very fair point that it is a big burden to put on a partner's shoulders, to expect them to be labor experts and great labor support people, with no training, possibly no experience, and a great deal of anxiety for their partner! So that was an interesting point.
I also found Chapter 9 to be very interesting. This chapter focused on a hospital in Dublin where every laboring woman got one-to-one care from a doula/midwife (actually, nurses who were training to be midwives). I was rather amazed by the amount of intensive coaching that was described, and a little bit disappointed by how strictly they seemed to coach pushing. I guess I can't fault their methods too much: the vast majority of first-time mothers delivering spontaneously and naturally within ~8 hours of being admitted to the hospital? Impressive!
Bottom line: Great book for someone who doesn't know much about doulas, or who is skeptical about them, to learn how great doulas can be. Great for someone who wants cold hard facts without "woo." Overall, I feel like this book is really aimed at people who want to know exactly what a doula does and exactly what the benefits are. It feels a little bit like a book for doctors, nurses, hospitals, medical providers, etc. Maybe not as useful for expectant parents as some of the other books are there, but again, good for expectant parents who want "just the facts!"