Fluidization is a crucial emergent feature of apparently solid-like epithelial cell layers, e.g., our skin, that allows these tissues to perform fundamental biological functions, like morphogenesis, healing a wound, responding to inflammations, etc. A common feature of these phenomena is the development of migratory behaviors of cells starting from a quiescent arrangement of cells in homeostasis. I will describe a general theoretical framework1 to understand the different mechanisms of such fluidization processes observed in a solid-like epithelial cell monolayer via the conventional epithelial-mesenchymal transition and an unconventional unjamming transition1, observed first in an asthmatic human lung epithelium. This model predicts the physical mechanisms and distinct features of these different processes1 based on the abilities of single cells to change shapes, cooperate with neighbors and generate forces for movement. I will also show how the scope of this model can be broadened2,3 to address various collective tissue behaviors observed in nature. Finally, I will provide an outlook on future questions regarding the mechanobiological relationship of the cell with their environment in tissues.