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 Recent observations across various species have revealed a rich phenomenology of epithelial mechanics arising from the active-viscoelasticity and turnover of the actomyosin cortex. However, a link between the subcellular cortical dynamics and the tissue scale response has been lacking in theoretical models of epithelia. For instance, in classical vertex models, a phenomenologically motivated work function governing the vertex dynamics (Alt et al, Philos. Trans. R. Soc. Lond., B, Biol. Sci., 2017) often lacks a direct connection to the microscopic subcellular physics. In this talk, I will present a new formalism, coined active-gel tissue model (AGTM), which bridges the active-gel models of the actomyosin cortex taking into account the active contractility of the cortex, the viscoelastic relaxation due network remodelling and the turnover of its constituents, with vertex-like models at a tissue scale. By solving the active gel on each of the curved faces of a 3D tissue, we show that this unified framework systematically links subcellular cortical dynamics with tissue mechanics, and ties to a common subcellular origin a number of seemingly disconnected dynamical tissue behaviours such as stress relaxation following step-strain manoeuvres (Casares et al., Nat. Mat. 2015, Khalilgharibi et al, Nat. Phys., 2019), buckling and transient buckling upon compression (Wyatt et al, Nat. Mat., 2020), pulsatile contractions during Drosophila dorsal closure (Solon et al, Cell, 2009), spontaneous curling (Fouchard et al, PNAS, 2020) and active superelasticity (Latorre et al, Nature, 2018). This framework is compatible with more elaborate dynamical models of the cytoskeleton, of adhesion complexes and their interaction, and thus serves as a general background for combining more complex multi-species models accounting for regulatory networks and junctional rearrangements, potentially providing a mechanistic understanding of active non-linear response of tissues with cell level resolution.