Theory and application of the CTOCD (Continuous Transformation of Origin of Current Density) method to the computation, visualisation and interpretation of ring-current aromaticity and antiaromaticity will be discussed. In this Ansatz (due to Keith and Bader), calculation of induced current density at any point in space takes that point as origin. It will be shown here that this 'ipsocentric' choice brings with it, in addition to computational economy, an important conceptual advantage: unique decomposition of properties into occupied-orbital contributions, free from unphysical mixing, and subject to selection rules based on orbital symmetry, energy and nodal characteristics. This leads to rationalisations of where the currents in aromatic systems come from, why they have the sense that they do, and how they are affected by changes in geometry, substitution and charge. Results for a range of π and σ systems will be presented and new applications to 'homo-aromatic' systems will be described.