Alison, Emily, Aria, Hanna, and Spencer used to be the best of friends in the 7th grade. That is, until Alison goes missing without a trace. Alison was the "Queen Bee" of the group and she knew all of the girls secrets. The girls admit that Ali could be nasty at times but she could really make you feel like you were the most important person in the world. After her disappearance, the remaining 4 girls drift far apart. 3 years later, they start receiving weird texts signed by an anonymous "A", which ultimately brings the girls back together as a group. 
 Okay, first thing that should be said is that I have watched Season 1 & 2 of the ABC family TV adaptation, but I've only read the first book of the series. Simply put, the show seems to be so much better than the book for many reasons. 
 Some people say that the TV show dragged on for so long and that it lost their interest. I have to disagree, because this first book dragged on and on and the girls don't reunite until the last chapter. In the show, they seem to reunite much quicker. 
 As another reviewer stated, there are many brand references, i.e. "Gucci sunglasses" "Coco Chanel" "Treo" (which was said about 10 times within 3 chapters). A handful of references like that is acceptable, if not preferable, but it got way out of hand and excessive. For instance, we don't need to know the brand of lipstick that Mona is applying while eating at a cafe. 
 There was also many alcoholic and smoking references in the book, much more than in the show. Yeah, I know that drinking and smoking does exist in the teenage world, as I am a teenager in these girls positions, but I felt that the show handled the topic much better, and it was not over-excessive. 
 Other than those points, this was an enjoyable read. Since I already bought the boxed set (#1-4), I will be reading the sequels. I also can't wait for Season 3 of the show!