In this talk I review attempts to build a self-consistent model for the dynamical state of the ISM in star-forming galactic discs. Ideally such a model would incorporate star formation, stellar feedback, gravitational instability, the maintenance of turbulence, and perhaps the transport of gas through the ISM, into a unified framework, simultaneously explaining the relation between gas content and star formation (the Kennicutt relation), the observed correlation between galaxies’ star formation rates and velocity dispersions, and a variety of other observations. I summarise the various ways that theorists have attempted to fit together physical ingredients to reach this goal, the differing physical pictures behind these models, and the strengths and weaknesses of each when it comes to reproducing the observations. I then show that it is possible to combine the best elements of these models into a single, unified picture that successfully reproduces most of the major observations. I suggest future observations and numerical experiments that can be used to test this unified model.