This present invention provides devices for the parallelization of the formation of droplets in a multiple droplet generator integrating two or more parallel flow-focusing devices (FFDs) with either identical, or different, geometries. In the parallel identical FFDs, emulsification generates droplets with a narrow (below 4%) polydispersity despite weak coupling between the identical flow-focusing devices. Formation of droplets in the integrated droplet generator comprising FFDs with different dimensions of the microchannels occurs with strong coupling between the FFDs and produces droplets with varying sizes and size distributions. For such devices the regime in which emulsification produces droplets with varying dimensions and a narrow size distribution have been identified. The results of this work can be used in scaling up the production of droplets and in the simultaneous production of droplets and particles with different dimensions.