In the biomedical sciences, where endless combinatorial diversity of genes, proteins and synthetic molecules is involved, miniaturisation has not simply allowed an increase in the speed at which experiment can be performed: it has given birth to new areas such as combinatorial chemistry and biology, proteomics, genomics, and more recently, systems and synthetic biology. In all these areas, the synthesis, assay and analysis of large molecular ensembles has become the essence of experimental progress. However, it is the systematic analysis of the enormous amounts of data generated that will ultimately lead to an understanding of fundamental chemical and biological problems. This proposal deals with approaches in which libraries of molecules are employed to give such mechanistic insight – into how enzyme catalysis is brought about in proteins and polymeric enzyme models and into the molecular recognition and cell biology of drug delivery reagents. In each case considerable technical challenges are involved in the way diversity is brought about and probed: ranging from either using the tools of synthetic chemistry to using gene repertoires in emulsion microdroplet reactors with femtolitre volumes, handled in microfluidic devices.