An introduction to the theory and practice of modern vacuum technology, with applications. Focuses on the understanding, operation, and selection of equipment for vacuum processes used in semiconductor, optical, and related technologies. This 2nd Edition has new information on components, lubrication, pump fluids, and other materials. Basic characteristics and operational procedures are given for each high-vacuum pumping system.
You can read my full summary here (website is unadvertised). It includes some things I felt were important that O'Hanlon left out and excludes some things from the book I felt weren't as important if you have a basic physics/chemistry background, e.g., gas properties).
If your career deals with vacuum, read this book cover-to-cover. O'Hanlon begins with the basics of gases (their properties, flow regimes, relation with solids) and progresses to actual vacuum concepts. The mathematics behind vacuum are included with explanations, as well as lay-person descriptions. While the descriptions are nice, I encourage the reader to search the internet for videos of how the various pumps operate, as it is much clearer than words and a static figure.
Third edition should be purchased if possible—the second edition was published before the invention of some important technology, e.g., scroll pumps.