Explore the intricate relationship between tissue mechanics and growth in this Rothschild Lecture by Professor Jean-Francois Joanny from the Collège de France. Delve into the crucial role mechanical properties play in tissue development, gene expression, and cancer progression. Examine how tissues behave as visco-elastic fluids at macroscopic scales, exhibiting unique active phenomena like spontaneous flows and turbulence. Investigate the microscopic perspective using the vertex model, revealing tissues as thixotropic and shear-thinning fluids under strong deformations. Gain insights into the absence of finite yield stress in tissues formed by dividing cells, as supported by numerical simulations.