We present temperature dependent high resolution resonant optical spectroscopy on a single, negatively charged InGaAs quantum dot. We performed laser transmission measurements yielding the natural linewidth of the excitonic ground state transition of a quantum dot in a temperature range from 4.2 K up to 25 K. Here, we describe the linewidth evolution and the temperature induced red shift of the resonance energy with simple models based on the exciton-phonon coupling in the quantum dot. The resonant spectroscopy measurements are complemented with results from non-resonant PL measurements on the very same quantum dot. Here we observe a simple linear behavior of the linewidth according to an effect of a fluctuating environment. © 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.