Hello. In my university the course of the Field theory was based on Landau's book, which of course, is a quiet rough book to introduce a subject with - so all I was left with was superficial knowledge of the branch. I would like to read another book (introductory level is preferred) about the subject to gain much stronger basic knowledge about the Field theory and then to use it as a foundation to re-read Landau's book to get a deeper insight in the theory. The book which contains very detailed derivation of Action, important tensors and etc. is just perfect.