“Voltage Droop” is a new concept that has been developed primarily for use in the harmonic current allocation process. Voltage droop offers the opportunity to both vastly simplify the procedures required by the present IEC 61000.3.6  guidelines for Stage 2 allocation and provide a solid theoretical base to this work. The voltage droop concept has also been found to provide a usefull theoretical basis for the harmonic standard IEEE 519. While this paper develops the voltage droop concept using diagrams and words, the companion paper “Harmonic Allocation Following IEC Guidelines Using the Voltage Droop Concept” contains a full critical mathematical description including an example. The voltage droop concept can be applied to radial, meshed and SWER distribution systems where feeders are sufficiently short that line capacitance can be ignored and all capacitor banks are detuned to prevent resonances at harmonic frequencies. The concept has application in HV, MV and LV systems. Use of the voltage droop concept for flicker allocation and unbalance studies is also briefly discussed.