Abstract We develop a general theory for spatio-temporal intensity correlation measurements for a scattered beam. A completely quantum mechanical description for both excitation and detection setup is used. Our description is essentially valid for weak incident light beams and single photon absorption processes. We describe from a unified point of view both, stationary as well as time resolved experiments. We emphasize the interest of such experiments in the study of processes like resonance Raman scattering and resonance fluorescence. We show, that for weak light beams, the property of photon bunching still exists in the scattered beam. Also we obtain an observable coherent contribution associated with different final levels of the target — atoms or molecules — a result which cannot be reached by intensity measurements.