A major challenge in biology is to unravel the organisation and interactions of cellular networks that enable complex life processes. The underlying complexity arises from dynamic interactions among large numbers of cellular constituents, such as genes, proteins and metabolites. The classical biochemistry and molecular biology approach has successfully identified most of the components and some interactions, but using such reductionist approach it is not possible to comprehend how system properties emerge. To understand how cells function, comprehensive and quantitative data on components and interactions are required on one hand, coupled with rigorous data integration and modelling on the other. The aim of this seminar is to explain the principles of experimental techniques for study of cell processes at the level of gene expression, protein composition and metabolite profile, in addition to studies of interactions between different components. The structure of data as well as reliability of the data obtained by different techiques will be discussed.