Numerous works are reported in literature concerning the biofilm growth on surfaces in seawater but the understanding of the adhesion mechanisms in the first steps of immersion is still subject to investigations. A knowledge of the chemical composition and of the kinetics of conditioning layer formation is a central requirement for a sound scientific understanding of biofilm growth. Due to its complexity and to the interdisciplinary nature of the subject, this research asks for the collaboration between the fields of material science, surface analyses, chemistry, marine microbiology and biochemistry. The first steps of biofilm formation on 316L stainless steels immersed in natural sea water have been studied, using a broad range of surface characterisation techniques : X-ray Photoelectron Spectroscopy (AR-XPS) for chemical characterisation of the passive film and of the adsorbed organic species, Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) for chemical characterisation of the adsorbed organic species, Surface Infra-Red Spectroscopy (IRRAS) for the description of the chemical links, Atomic Force Microscopy (AFM) for the identification of the morphology, thickness and homogeneity of the organic film, and liquid drop contact-angle measurements for the determination of the hydrophilic/hydrophobic and acido-basic character of the outer surface.