Hydrogels, with their three-dimensional hydrophilic polymer networks, are increasingly used in biomedical applications, including drug delivery, tissue engineering, and wound healing. This review discusses the classification of hydrogels based on cross-linking methods, their synthesis, properties, and applications. It highlights recent advancements in hydrogel-based drug delivery systems, including oral, injectable, topical, and ocular approaches, emphasizing their role in improving therapeutic outcomes. Challenges in clinical translation, such as immunogenic responses and by-product removal, are addressed, along with future directions for personalized medicine and regenerative healthcare. Hydrogels are categorized into physical and chemical types, with physical hydrogels formed through non-covalent interactions and chemical hydrogels through covalent bonds. Physical hydrogels are sensitive to environmental stimuli, while chemical hydrogels offer greater stability and control. The review also explores the characterization of hydrogels, including mesh size, swelling behavior, porosity, microstructure, mechanical properties, and degradability. These properties are crucial for effective drug delivery, with methods for measuring them discussed. The review highlights the potential of hydrogels in drug delivery, including their use in oral, injectable, topical, and ocular applications, and their ability to respond to environmental stimuli for targeted drug release. Challenges in hydrogel development, such as mechanical stability and biodegradability, are addressed, along with future directions for improving hydrogel-based drug delivery systems. The review underscores the transformative potential of hydrogels in biomedical engineering, emphasizing the need for ongoing innovation to address existing challenges and unlock new therapeutic opportunities.Hydrogels, with their three-dimensional hydrophilic polymer networks, are increasingly used in biomedical applications, including drug delivery, tissue engineering, and wound healing. This review discusses the classification of hydrogels based on cross-linking methods, their synthesis, properties, and applications. It highlights recent advancements in hydrogel-based drug delivery systems, including oral, injectable, topical, and ocular approaches, emphasizing their role in improving therapeutic outcomes. Challenges in clinical translation, such as immunogenic responses and by-product removal, are addressed, along with future directions for personalized medicine and regenerative healthcare. Hydrogels are categorized into physical and chemical types, with physical hydrogels formed through non-covalent interactions and chemical hydrogels through covalent bonds. Physical hydrogels are sensitive to environmental stimuli, while chemical hydrogels offer greater stability and control. The review also explores the characterization of hydrogels, including mesh size, swelling behavior, porosity, microstructure, mechanical properties, and degradability. These properties are crucial for effective drug delivery, with methods for measuring them discussed. The review highlights the potential of hydrogels in drug delivery, including their use in oral, injectable, topical, and ocular applications, and their ability to respond to environmental stimuli for targeted drug release. Challenges in hydrogel development, such as mechanical stability and biodegradability, are addressed, along with future directions for improving hydrogel-based drug delivery systems. The review underscores the transformative potential of hydrogels in biomedical engineering, emphasizing the need for ongoing innovation to address existing challenges and unlock new therapeutic opportunities.