This book is useful to those who are fairly well-versed in CMMI. For me, this is by far the best "reference" material, since it is concise, and it consolidates separate points into a table or a 1-pager with diagrams, making it easier to digest and understand. This is especially so when compared with the thick (700+ pages) big (A4 size) tome official guidebook from SEI. I could easily take Ahern onto the plane / train for quick brush-up on particular process areas. I would recommend this book to those who had already gained some CMMI knowledge, and would need a light handbook for quick reference.