Emanuel Tov’s Text-Critical Use of the Septuagint in Biblical Research is a key text in Septuagint studies. But it’s been out of print… until now. Eisenbrauns has just published a “Completely Revised and Expanded” third edition of the book.
Here’s the publisher’s write-up:
This handbook on the Septuagint (LXX) provides a practical guide for the student and scholar alike in the perusal of that translation in the text-critical analysis of the Hebrew Bible. It does not serve as another theoretical introduction to the LXX, but it provides all the practical background information needed for the integration of the LXX in biblical studies. The LXX remains the most significant source of information for the study of ancient Scripture together with the Masoretic Text and several Qumran scrolls, but this translation is written in Greek and many technical details need to be taken into consideration when using this tool. The author presents this handbook after half a century of study of the Septuagint, four decades of specialized teaching experience in that area, and involvement in several research projects focusing on the relation between the Hebrew and Greek Bibles.
The first two editions of this handbook, published by Simor of Jerusalem (Jerusalem Biblical Studies 3  and 8 ), received much praise but have been out of print for a considerable period. This, the third, edition presents a completely revised version of the previous editions based on the many developments that took place in the analysis of the Septuagint, the Hebrew Bible and the Qumran Scrolls.
I’d link to the book on Amazon, but you really should just buy directly through Eisenbrauns. They are good folk, make great resources, and have put this book on sale now. Get it here. You can also find a PDF info sheet (with Table of Contents) here.