This chapter presents an overview of microfluidic devices reported in the literature, used to develop methodologies for nucleation of biomolecules, with crystal size control, and for collecting thermodynamic and kinetic data. Section 2 is dedicated to the properties of microfluidic devices through materials used for their fabrication and for crystal analysis. Section 3 describes the variety of microfluidic devices available and how to handle them to produce flows, droplets, and/or wells of micrometer size. These devices use crystallization methods inspired by batch processes, and they are mainly used for protein crystallization. Section 4 focuses on fundamental properties of biomolecule crystallization determined using droplet-based microfluidics: nucleation kinetics, nucleation rate, and effective interfacial energy crystal/solution. Section 5 explains how the kinetic effect of confinement due to micrometer size, and so nanovolumes, leads to isolation of different phases. These latter are characterized by X-ray diffraction (XRD), and methods to minimize manual handling of crystals for XRD are also presented, with appropriate equipment to store the crystals.