Hydrogels have been used for biomedical applications in recent decades. They are a perfect candidate for regenerative medicine as they resemble the extracellular matrix of native tissues. In addition, their highly hydrated structure makes them a suitable choice for drug and other therapeutics delivery. Injectable hydrogels have increasingly gained attention due to their capability for homogeneous mixing with cells and therapeutic agents, minimally invasive administration, and perfect defect filling. In this review, we discuss various mechanisms which facilitate injectability of hydrogels, including in situ gelling liquids, injectable gels, and injectable particles. Then, we explore the biomedical applications of injectable hydrogels, including tissue engineering, therapeutic agent delivery, and medical devices.