Variability of the Australian monsoon onset, termination, and strength was investigated in terms of the first five major modes of monsoon precipitation found via cyclostationary empirical orthogonal function analysis. They are the El Ni¿o--Southern Oscillation (ENSO) mode, the seasonal cycle, the ENSO transition mode, and the two Madden-Julian oscillation (MJO) modes, respectively. Whereas the seasonal cycle defines the fixed onset (~5 January) and termination (~5 March) dates, the presence of the other modes alters these dates. The impact of each mode was investigated after each mode, with a strength corresponding to 1 standard deviation of its variability, was added to or subtracted from the mean seasonal cycle. It is shown that the contribution of each mode to the monsoon precipitation is geographically complex and varies significantly throughout the monsoon period. One striking feature is that the impact of each mode is highly asymmetric with respect to its phase. The negative modes generally affect more significantly the onset, the termination, and the amount of monsoon precipitation. Although each of the four modes makes a unique and tangible contribution, the ENSO mode contributes most significantly to the overall mean and variance of the monsoon precipitation variability. While the positive ENSO (El Ni¿o) mode does not seriously alter the onset and termination times, the negative ENSO (La Ni¿a) mode prolongs the duration of the Australian summer monsoon significantly. Although the contribution to the overall mean is small, the two MJO modes are the most dominating factor controlling the onset and termination times of the Australian summer monsoon.