Quantum field theory remains among the most important tools in defining and explaining the microscopic world. Recent years have witnessed a blossoming of developments and applications that extend far beyond the theory's original scope. This comprehensive text offers a balanced treatment, providing students with both a formal presentation and numerous practical examples of calculations. This two-part approach begins with the standard quantization of electrodynamics, culminating in the perturbative renormalization. The second part comprises functional methods, relativistic bound states, broken symmetries, nonabelian gauge fields, and asymptotic behavior. Appropriate for students and researchers in field theory, particle physics, and related areas, this treatment presupposes a background in quantum mechanics, electrodynamics, and relativity, and it assumes some familiarity with classical calculus, including group theory and complex analysis.