Scale Free Processes in Stellar Cluster Formation

We review some of the basic population properties of stellar clusters, as well as how they relate to star-formation more broadly within their host galaxies. Despite the common assertion, the vast majority of stars do not form within stellar clusters. For typical galaxies (including the solar neighbourhood), the fraction of stars forming in clusters is ~10%. There are indications however that this fraction increases as a function of increasing star-formation rate surface density, in agreement with model predictions (based on a turbulent ISM and relatively straight-forward prescriptions of star-formation).