From a survey of the literature on lightning characteristics, we present and discuss our recommendations for the median (50%) and severe (1%) values of the salient parameters of lightning current in both positive and negative cloud-to-ground discharges. We present general expressions, suitable for numerical simulation of lightning effects, for lightning current versus time, current derivative versus time, second current derivative versus time, charge transfer versus time, and action integral (specific energy) versus time. We give sets of constants for these expressions such that the resultant waveforms for positive and negative flashes and for their component strokes and continuing current exhibit approximately the median and severe lightning current parameters recommended, and otherwise resemble the measured waveforms found in the literature.