Luminescence intensity autocorrelation (LIA) is employed to investigate coupling dynamics between (In, Ga)As quantum dots (QD's) and a high-Q (∼7000) resonator with ultrafast time resolution (150 fs), below and above the lasing threshold at T = 5 K. For QD's resonant and nonresonant with the cavity we observe both a sixfold enhancement and a 0.77-time reduction of the spontaneous emission rate, respectively. In addition, L1A spectroscopy reveals the onset of coherent coupling at the lasing threshold through qualitative changes in the dynamic behavior and a tripling of the resonant QD emission rate.