Density functional theory (DFT) provides a convenient framework for quantitative computations of the electronegativity X of atoms and ions. ~ is justthe negative of the chemical potential ~t of DFT. In this paper we study ) using simple versions of the DFT within the original spirit of DFT, that is, working with the electron density ~(~) as the fundamental ingredient. We show that density gradient terms must be taken into account to obtain results of qualitative or semiquantitative value. Apart from the study of the electronegativitiy of atoms and ions corresponding to several groups of the Periodic Table, the virtues of using DFT are illustrated by a number of selected applications: a) The electronegativity of exotic atoms containing unsaturated quarks attached to the nucleus, b) The consequences of electronegativity equalization for charge transfer in molecule formation. The relations between electronegativity, the electrostatic potential in the atom and bond distances are also explored following ideas originally put forward by Politzer. c) Finally, and due to its importance in catalytic processes, we make a start on the study of the electronegativity of small metallic particles.