Two aspects are quintessential if one seeks to successfully perform DFT calculations: a basic understanding of how the concepts and models underlying the various manifestations of DFT are built and an essential knowledge of what can be expected from DFT calculations and how to achieve the most appropriate results. This chapter expands on the development and philosophy of DFT and aims to illustrate the essentials of DFT in a manner that is intuitively accessible. An analysis of the performance and applicability of DFT focuses on a representative selection of chemical properties, including bond lengths, bond angles, vibrational frequencies, electron affinities and ionization potentials, atomization energies, heats of formation, energy barriers, bond energies, hydrogen bonding, weak interactions, spin states, and excited states.