Density Functional Theory: Fundamental Theory, Key Methods, and Applications provides a thorough and detailed explanation and overview of this important computational quantum mechanical modeling method and its applications. The book's chapters are structured to be easier to understand and more accessible to the target audience. Split into three distinct sections, it examines foundational knowledge surrounding DFT, covering key concepts such as the Thomas-Fermi model and Hohenberg-Kohn-Sham theory, exchange-correlation functionals, the advantages and disadvantages of DFT compared to MO theory, and other methods before exploring areas of future DFT development. The second section then examines practical methods and approaches for DFT, looking at the types of density functionals such as LSDA, GGA and meta-GGA functionals, hybrid functionals, DFTB methods, dispersion corrected functionals, Time-Dependent DFT, and the Plane-wave approach. It also looks at relations between DFT and ab initio molecular dynamics and the QM/MM approach. The final section then focuses on applications and some useful case studies of use of DFT in different areas, whilst weighing up strengths and weaknesses in such applications.