The present invention generally relates to systems and methods of forming particles and, in certain aspects, to systems and methods of forming particles that are substantially monodisperse. Microfluidic systems and techniques for forming such particles are provided, for instance, particles may be formed using gellation, solidification, and/or chemical reactions such as cross-linking, polymerization, and/or interfacial polymerization reactions. In one aspect, the present invention is directed to a plurality of particles having an average dimension of less than about 500 micrometers and a distribution of dimensions such that no more than about 5% of the particles have a dimension greater than about 10% of the average dimension, which can be made via microfluidic systems. In one set of embodiments, at least some of the particles may comprise a metal, and in certain embodiments, at least some of the particles may comprise a magnetizable material. In another set of embodiments, at least some of the particles may be porous. In some embodiments, the invention includes non-spherical particles. Non-spherical particles may be formed, for example, by urging a fluidic droplet into a channel having a smallest dimension that is smaller than the diameter of a perfect mathematical sphere having a volume of the droplet, and solidifying the droplet, and/or by exposing at least a portion of a plurality of particles to an agent able to remove at least a portion of the particles.