This book offers an in-depth exploration of both natural and synthetic polymeric hydrogels and bioinks, with a focus on their groundbreaking use in medical applications, particularly in the production of 3D tissue constructs and organ models. It covers the science and applications of hydrogels, beginning with a foundational understanding of tissue engineering and scaffold types. It describes the versatile 3D printing techniques that bring bioinks to life, followed by in-depth analyses of natural and synthetic hydrogels. Special emphasis is placed on hydrogels that mimic the extracellular matrix, providing crucial insights for researchers working to create realistic tissue environments. From smart hydrogels with adaptive properties to injectable solutions and conductive formulations, this book highlights innovations that are transforming therapeutic strategies. The text also covers a range of biomedical applications, including hydrogels in controlled delivery systems, nerve, cartilage, bone, skin, and cornea therapies, and their use in producing contact and intraocular lenses. Meticulously curated by leading experts in the field, this volume bridges the gap between cutting-edge research and practical applications, making it an essential guide for advancing tissue engineering and regenerative medicine.