Biomaterials are non viable materials used as medical devices interacting with biological systems and are increasingly being applied as substitutes and/or sensors in human hosts. This paper describes the specific surface functionalization and characterization of biomaterials for Medical Applications by use of methods such as x-ray photoelectron spectroscopy (XPS) and imaging time-of-flight secondary ion mass spectrometry (ToF-SIMS) as well as contact angle measurements and scanning force microscopies (SFM). Bio-molecules (peptides, polysaccharides, proteins, etc) are grafted to various types of materials ranging from metals, semiconductors to polymers. It is the bulk composition which determines the physical, mechanical and rheological properties, whereas surface chemistry and topography influence the response to a foreign implant. The control of chemistry, forces and topography of surfaces and thin films with femtomol sensitivity, nanometer in-depth information and submicron lateral resolution will be highlighted. Practical applications cover photo-grafting of hydrocarbons for the development of bio-sensors - glycoengineering -, plasma modification of polymers to reduce bacterial adhesion on endotracheal devices and cell adhesion on metallic surfaces. References: 1. D. Leonard and H.J. Mathieu, Fresenius' Journal Analytical Chemistry 365 (1999) 3-11 2. H. J. Mathieu, Surface and Interface Analysis 32 (2001) in print.