You saw it first in Rounders (you did see Rounders right?). In recent years, we have seen a fresh supply of books regarding poker tells, but Mike Caro's Book of Poker Tells (BoPT) is the classic that started it all.

First off, if you are strictly an online player there isn't much value here because Caro focuses almost entirely on physical tells. Maybe the day will come when our physical likeness will be projected onto the online tables instead of avatars, but until then, you can find better material for your money.

For the live player, or the recreational home game, BoPT is a must-read. Caro divides the content into two main categories.

1) "Tells from those who are unaware"
This section focuses on the unconscious, physical mannerisms that your opponents (and maybe even you) may be giving off. Did your opponent's hands just start trembling? Did they just glance at their chips? How do they stack their winnings?

2) "Tells from actors"
This is the opposite of the previous section. It describes the various conscious actions that players perform in order to deceive you at the tables. Is your opponent already reaching for chips? Are they seemingly staring off into space? Why are their cards practically in the muck already?

For every tell (over 50 in total), Caro includes a description, the reasoning behind it, and a reliability factor. He then follows it up with picture-by-picture analysis as the tell unfolds from beginning to end. He also includes 25 laws that allow easier memorization of the example tells. At the end, there is a photo quiz to test you on the book's content.

Overall, while much of Caro's BoPT may be common knowledge or expanded upon in other poker tell books, it remains the original on the subject and not reading it is like pitching in more rake, definitely -EV.