This review examines the preparation of alginate hydrogel microparticles. We focus on droplet-based microfluidics, a technique widely employed for its ease of use and excellent control of physicochemical properties, with narrow size distribution. Alginate hydrogel microparticles are obtained by conducting “on-chip” and/or “off-chip” gelation. Various strategies are described and compared. Microparticle properties such as size, shape, concentration, stability and mechanical properties are discussed. Finally, we consider future perspectives for the preparation of hydrogel microparticles and their potential applications.