The importance and the beauty of modern quantum field theory resides in the power and variety of its methods and ideas, which find application in domains as different as particle physics, cosmology, condensed matter, statistical mechanics and critical phenomena. This book introduces the reader to the modern developments in a manner which assumes no previous knowledge of quantum field theory. Along with standard topics like Feynman diagrams, the book discusses effective lagrangians, renormalization group equations, the path integral formulation, spontaneous symmetry breaking and non-abelian gauge theories. The inclusion of more advanced topics will also make this a most useful book for graduate students and researchers.
A very mathematical introduction to QFT. After the first four chapters, I felt I finally understood the fundamentals- along with several other topics I'd been trying and failing to understand: Lie groups, gauge symmetries etc. I recommend this text above others simply because it was the first to finally make sense to me, although the approach may be a little too abstract in general.
Maggiore introduces representations on symmetry groups to motivate the introduction of the spinor, whose properties follow as a result. Generalizing this to Dirac and Majorana spinors, then fields, allows the construction of a field theory with Lorentz invariance. I found this approach to be elegant.