Injectable hydrogels have shown great potential for cartilage and bone tissue engineering due to their high water content, similarity to the natural extracellular matrix (ECM), porous structure for cell transplantation and proliferation, minimal invasiveness, and ability to match irregular defects. This review discusses the selection of appropriate biomaterials and fabrication methods for preparing novel injectable hydrogels for cartilage and bone tissue engineering, as well as the biology of cartilage and the bony ECM. It also explores future perspectives for injectable hydrogels in cartilage and bone tissue engineering. Cartilage and subchondral bone damage can result from trauma, arthritis, and sports injuries. Cartilage has limited self-healing capacity due to its lack of vascularization, innervation, and progenitor cells. Bone, although highly vascularized, has limitations in repair due to donor-site morbidity, infection risks, and high nonunion rates. Bone defects are a leading cause of morbidity and disability in the elderly. Tissue engineering, which emerged in the 1990s, has become a common approach for cartilage and bone tissue reconstruction and regeneration. Engineered tissues consist of scaffolds, cells, and growth factors. Ideal scaffolds should be porous, biocompatible, non-toxic, and capable of promoting cell differentiation and new tissue formation. They should also have stable mechanical properties, degrade in response to new tissue formation, and facilitate nutrient and metabolite diffusion. Various biomaterials, both natural and synthetic, have been explored for injectable hydrogel preparation. Natural biomaterials include chitosan, collagen/gelatin, alginate, fibrin, elastin, heparin, chondroitin sulfate, and hyaluronic acid. Synthetic biomaterials include PEG, poly(L-glutamic acid), poly(vinyl alcohol), poly(propylene fumarate), and others. Injectable hydrogels can be fabricated through physical or chemical methods. Physical hydrogels are formed by weak secondary forces, while chemical hydrogels are formed by covalent cross-linking. Injectable hydrogels can be classified into enzymatically cross-linked, photo-cross-linked, Schiff base cross-linked, Michael addition-mediated, click chemistry-mediated, ion-sensitive, pH-sensitive, and temperature-sensitive hydrogels. Injectable hydrogels have attracted attention for their ability to replace implantation surgery with a minimally invasive injection method and to form any desired shape to match irregular defects. Excellent biomaterials and appropriate fabrication methods are crucial for developing ideal injectable hydrogels. Various biomaterials have been exploited to prepare injectable hydrogels, including chitosan, collagen/gelatin, alginate, fibrin, elastin, heparin, chondroitin sulfate, and hyaluronic acid. Injectable hydrogels can be fabricated through physical and chemical methods. Physically injectable hydrogels are spontaneously formedInjectable hydrogels have shown great potential for cartilage and bone tissue engineering due to their high water content, similarity to the natural extracellular matrix (ECM), porous structure for cell transplantation and proliferation, minimal invasiveness, and ability to match irregular defects. This review discusses the selection of appropriate biomaterials and fabrication methods for preparing novel injectable hydrogels for cartilage and bone tissue engineering, as well as the biology of cartilage and the bony ECM. It also explores future perspectives for injectable hydrogels in cartilage and bone tissue engineering. Cartilage and subchondral bone damage can result from trauma, arthritis, and sports injuries. Cartilage has limited self-healing capacity due to its lack of vascularization, innervation, and progenitor cells. Bone, although highly vascularized, has limitations in repair due to donor-site morbidity, infection risks, and high nonunion rates. Bone defects are a leading cause of morbidity and disability in the elderly. Tissue engineering, which emerged in the 1990s, has become a common approach for cartilage and bone tissue reconstruction and regeneration. Engineered tissues consist of scaffolds, cells, and growth factors. Ideal scaffolds should be porous, biocompatible, non-toxic, and capable of promoting cell differentiation and new tissue formation. They should also have stable mechanical properties, degrade in response to new tissue formation, and facilitate nutrient and metabolite diffusion. Various biomaterials, both natural and synthetic, have been explored for injectable hydrogel preparation. Natural biomaterials include chitosan, collagen/gelatin, alginate, fibrin, elastin, heparin, chondroitin sulfate, and hyaluronic acid. Synthetic biomaterials include PEG, poly(L-glutamic acid), poly(vinyl alcohol), poly(propylene fumarate), and others. Injectable hydrogels can be fabricated through physical or chemical methods. Physical hydrogels are formed by weak secondary forces, while chemical hydrogels are formed by covalent cross-linking. Injectable hydrogels can be classified into enzymatically cross-linked, photo-cross-linked, Schiff base cross-linked, Michael addition-mediated, click chemistry-mediated, ion-sensitive, pH-sensitive, and temperature-sensitive hydrogels. Injectable hydrogels have attracted attention for their ability to replace implantation surgery with a minimally invasive injection method and to form any desired shape to match irregular defects. Excellent biomaterials and appropriate fabrication methods are crucial for developing ideal injectable hydrogels. Various biomaterials have been exploited to prepare injectable hydrogels, including chitosan, collagen/gelatin, alginate, fibrin, elastin, heparin, chondroitin sulfate, and hyaluronic acid. Injectable hydrogels can be fabricated through physical and chemical methods. Physically injectable hydrogels are spontaneously formed