Injectable hydrogels are increasingly popular among researchers because of their in situ formability, in situ drug delivery, high targeting, and the ability to allow uniform incorporation of therapeutic molecules and/or cells without the need for surgery. At the same time, injectable hydrogels have good biocompatibility and biodegradability, resulting in fewer side effects. As a result, they have been used widely in biomedical applications such as tissue engineering and drug delivery. This review summarizes the current state of research in injectable hydrogels, highlights the synthesis of injectable hydrogels and their applications in the biomedical field, and provides some insights into the future development of injectable hydrogels.