Using time-resolved fluorescence spectroscopy, we have monitored the coalescence of polymer particles during the film formation process. The accessible parameters are the efficiency of fluorescence resonance energy transfer (FRET) between donor-labeled and acceptor-labeled particles, the scattering intensity, and the fluorescence lifetime of the donor in the absence of the acceptor. The FRET efficiency substantially increases during drying, even though the glass temperature of the material is around the drying temperature. This finding evidences polymer interdiffusion across the interparticle boundaries even without high-temperature annealing. Both the FRET efficiency and scattering intensity show a sigmoidal dependence on drying time. The transition times of the two curves coincide for soft materials, whereas they differ for materials with a T, around the drying temperature. In the latter case, the FRET efficiency-probing interparticle contact-goes through the transition earlier than the scattering intensity and the donor lifetime. Cohesive interparticle contacts form before the end of the compactification stage, thereby reducing the likelihood of crack formation during drying.