This volume is based on the proceedings of a NATO-Gulbenkian Foundation sponsored Summer School held in May-June 1982 in Sintra­ Estoril, Portugal. Given the accelerated growth of knowledge in the field of eukaryotic gene expression, it seemed timely to hold a NATO Advanced Study Institute to discuss current developments in this area of biology and to evaluate the potential of emerging technologies such as gene transfer, recombinant DNA cloning and quantitative high resolution two-dimensional gel electrophoresis. The initial articles in t~is volume describe various differentiation models and address questions such as the relationships between differentiation and cell proliferation, biochemical changes accompanying differen­ tiation, expression of differentiated gene products and their regulation as well as gene organization of cytoskeletal proteins. The second section describes properties of neoplastic cells, surveys current assays for transformation and offers some new insights into the mechanisms involved in carcinogenesis. The third part is dedicated to viral oncogenesis and to the role of onco­ genes in cell transformation. Particular emphasis is given to the role of tyrosine kinases in cell transformation. The concluding section deals with various aspects of gene expression in normal and transformed cells with special emphasis given to studies using two dimensional gel electrophoresis, cell hybridization, gene transfer and immunological techniques.