I need an introductory book on Conformal Field Theory

[Omega137]

Can anybody suggest a good introductory book on CFT.

I would like to learn String Theory; and this is my basic motivation to learn CFT...

 

[Demystifier]

Most textbooks and introductory lectures on string theory contain an introductory chapter on CFT.
For example, you may start with
http://xxx.lanl.gov/abs/hep-th/9411028

The above should be enough for most applications of CFT to string theory, but if you want an advanced text dealing only with CFT, I recommend
http://xxx.lanl.gov/abs/hep-th/9108028