I will discuss Onsager’s variational principle, an extension by Onsager of the principle of least energy dissipation by lord Rayleigh. Resorting to examples in biology, I will show that this variational approach is a very effective formalism to describe linear and non-linear non-equilibrium processes combining multiple physical phenomena. In particular, I will show how this principle can be employed to derive the governing equations that regulate the fracking of cell adhesions by osmotic pressure. Finally, I will show that this principle provides a direct route for the time and space discretisation of the equations needed for numerical simulations.