In the past five years the Max Planck Research Group for Nonlinear spectroscopy of bio-interfaces has worked at the intersection of surface science, nonlinear optics and soft and biological matter. For hard matter there is molecular level understanding of the surface region. This has enabled researchers to develop the highly complex structures that are nowadays found in (e.g.) computers, and mobile phones. Although biological and soft systems (such as liquid droplets, nanoparticles, liposomes, and viruses) are ubiquitous in our daily lives, our understanding is often limited to macroscopic theories. Consequently, the level of control of soft and biological matter is largely empirical and far behind that of hard matter. To initiate a change, we have in the past period worked on three main themes: (i) The investigation of structure and properties of biologically and medically relevant interfaces (supported lipid bilayers, biopolymer interfaces, water, protein-surface interactions). (ii) Development of nonlinear light scattering techniques as probes for molecular structure at the interfaces of small particles. (iii) The study of molecular interfacial structure, kinetics and dynamics of water, surfactants, phospholipids, sugars and peptides on small objects (nano-droplets, vesicles) in suspensions. The result of our work on these themes is summarized for this special issue article. © Carl Hanser Verlag GmbH & Co. KG.