The embryonic development of tissues is a dynamic process coordinated by intercellular signalling that direct gene regulatory networks to assign cell fate. At the same time tissue growth and differentiation alters the arrangement and number of cells, contributing to the elaboration of pattern. Together these mechanisms determine the pattern, pace, precision, and proportion of forming organs. Hence, accurate development and the specification of specialised cell types relies on the interplay of cellular and molecular processes. To understand this, quantitative approaches together with predictive and dynamical models are needed that allow the analysis of cellular differentiation dynamics and to determine principles of tissue development.