Small molecules could be easily handled, stored, delivered, and released from polyelectrolyte capsules. In order to make polyelectrolyte capsule a universe delivery platform, its permeability needs to be controlled. On the one hand, for efficient small-molecule encapsulation, the permeability of capsules should be significantly decreased. On the other hand, once the capsule reaches its target, the release of encapsulated materials needs to be triggered. These two functions-reducing permeability of capsules for encapsulation and subsequent release, collectively called tuning capsule permeability-are the subject of this chapter. This chapter demonstrates the possibility of entraping water-soluble molecular species into polyelectrolyte capsules modified by low-permeable dense polymers, e.g. polypyrrole, and various schemes for subsequent release of encapsulated materials. Future applications of polyelectrolyte capsules, such as carriers for gases, volatiles and, biomedically relevant molecules in pharmacy, food and gas industries, agriculture, and cosmetology, are also discussed.