Book excerpt: This book provides detailed information on the surface and surface chemistry of various biointerfaces for the understanding and development of biosensors, biocompatible devices, and drug delivery systems. It highlights the role of interfacial phenomena towards the behaviour of biomolecules on different surfaces and their significance in recent applications. The book also addresses various surface engineering techniques for the modification of biomaterials that are implemented for improving biocompatibility. It provides an updated scientific concept of various interactions of biological systems with surfaces/modified surfaces at the molecular and cellular level. The chapters include various in-vitro, in-vivo, ex-vivo models to illustrate various aspects of Biointerface Engineering. Finally, the book elucidates troubleshooting strategies and future prospects of Biointerface Engineering in Medical Diagnostics and Drug Delivery.