The present invention generally relates to microparticles and, in particular, to systems and methods for encapsulation within microparticles. In one aspect, the present invention is generally directed to microparticles containing entities therein, where the entities contain an agent that can be released from the microparticles, e.g., via diffusion. In some cases, the agent may be released from the microparticles without disruption of the microparticles. The entities may be, for instance, polymeric particles, hydrogel particles, droplets of fluid, etc. The entities may be contained within a fluid that is, in turn, encapsulated within the microparticle. The agent may be released from the entity into the fluid, and then from the fluid through the microparticle. In such fashion, the release of agent from the microparticle may be controlled, e.g., over relatively long time scales. Other embodiments of the present invention are generally directed to methods of making such microparticles, methods of using such microparticles, microfluidic devices for making such microparticles, and the like.