In this thesis the interaction between a single quantum dot and a cavity is investigated. Quantum dots embedded in a micropillar cavity are investigated by measuring the spectra, and by performing time-resolved measurements. The enhancement of the spontaneous decay of the quantum dot is measured to 18.9 with a resonant lifetime of 28.1 ps under the assumption of an exponential decay. A model is constructed with measurable parameters, and the calculated decay curves are not exponential. As a result the mean decay rate, which coincides with the exponential rate for an exponential decay, is calculated for the measured rates. A large deviation is seen, with an enhancement of the mean decay rate of 9.1 with a resonant lifetime of 56.5 ps. The non-exponential decay of the quantum dot is caused by non- Markovian processes in the dot-cavity interaction. Furthermore, the second order coherence is measured to determine the quality of the single-photon emission, and two-photon interference measurements are likewise performed. These measurements show an indistinguishability of 48%. Finally, cavity-assisted resonant excitation of a quantum dot with another quantum dot is demonstrated.