Powered by relativistic jets of matter speeding towards us almost head-on at the speed of light, radiating exclusively through extreme, non-thermal particle interactions, energized by accretion onto supermassive black holes, blazars are the most active of galaxies. Despite intensive observational and theoretical efforts over the last four decades, the details of blazar astrophysics remain elusive to this day. The primary reason is that small variations in the angle between blazar jet and line of sight produce a vast range of observed properties and associated blazar “phenotypes.” The unifying features that would illuminate the basic blazar physics are thus obscured. To overcome this difficulty, blazars have to be understood as a population rather than on an object-by-object basis. Here, we propose to build a phenomenological bridge between theoretical blazar models, and the multitude of high-quality observations of large samples of blazars that are currently being accumulated. We will do this by constructing sophisticated models for the statistical description of the observable properties of different blazar families, and by connecting them with both blazar theory and observations. Our project has the following specific research objectives: (a) to develop a robust and all-inclusive formalism for the statistical description of the blazar population; (b) to identify correlations between measures of blazar behaviour and physical properties of the jet-host system, which can reduce the number of independent variables in the description of the blazar population; and (c) to connect phenomenological population models to physical models of increasing complexity. The fellow will lead this project during the first four years of her return to Europe, where she will take up an Assistant Professor position at the University of Crete; the support through this fellowship will be thus essential for building her research group and her integration in the European Research Area.