Injectable hydrogels are a unique class of hydrogels that are formed upon injection into living bodies. They possess features of typical hydrogels such as softness, 3D network structures, large contents of water, the ability to load water-soluble substances, and so on. Furthermore, their injectability allows injectable hydrogels to be implanted into living bodies using a syringe in a minimally invasive way. After being loaded with different active substances (drugs, proteins, genes, viruses, cells, etc.), injectable hydrogels have been demonstrated to be potential in many different biomedical applications including controlled release and tissue engineering. However, biodegradability is also an important property of injectable hydrogels and allows removal of the hydrogels after accomplishment of their tasks. In this Perspective, we aim at introducing several different types of biodegradable and injectable hydrogels and compare their differences in properties and applications. Lastly, we also point out some remaining problems and future trends in the field of biodegradable and injectable hydrogels.