Embryonic organoids are self-organizing stem-cell systems that reproduce key features of early development, including symmetry breaking, differentiation, collective cell motion and tissue elongation, and can progressively generate structures resembling early organ-like domains. Their morphogenesis results from a strong coupling between cell fate and mechanics: stem cells continuously integrate biochemical and physical information from their local microenvironment and, in response, choose whether to remain undifferentiated or differentiate toward distinct cell types. These fate decisions in turn modify cell adhesion, contractility, motility and tissue organization. The aim of this internship is to bridge several physical scales: from single-cell properties and cell-cell interactions, to collective dynamics and a continuum description of the tissue. We will combine quantitative live imaging, image and data analysis, mechanical perturbations and biophysical modelling to understand how local mechanical properties, cell-state decisions and interactions between neighbouring cells generate non-trivial tissue-scale behaviours such as flows, spreading, polarization and elongation. The objective is to identify the physical mechanisms that connect cell-scale decisions to the global morphogenesis of embryonic organoids.