Inhomogeneous Cosmologies IV, Torun, 14-19 July 2019 During 14-19 July 2019 we are gathering experts in inhomogeneous cosmology for a small workshop of about 30 participants at Nicolaus Copernicus University in Torun, the town where Copernicus was born. We wish to map out the most promising directions for analytical, numerical and observational investigations aimed to take into account both structure formation and cosmological expansion within the constraints of general relativity. Can we clarify the physics present in the relativistic cosmology software now being developed? Are the calculations artificially constrained or are they fully relativistic? Can we achieve accurate postdiction of cosmological observations and follow up by making predictions for the upcoming decade of new major survey projects? We expect vigorous, constructive debate between "one-percenters" and "order-unity" proponents, and practical hands-on sessions of free-licensed inhomogeneous cosmology software packages. Feel free to redistribute this announcement. Check the CosmoTorun19 website or subscribe to the inhom newsletter to know when registration is open. More info: https://cosmo.torun.pl/CosmoTorun19 Newsletter 'inhom': https://cosmo.torun.pl/mailman/listinfo/inhom Contact: cosmotorun19 at cosmo.torun.pl Organising committee: Boud Roukema, Eloisa Bentivegna, Krzysztof Bolejko, Thomas Buchert, Mikolaj Korzyński, Hayley Macpherson, Jan Ostrowski, Sebastian Szybka, Eleonora Villa, David Wiltshire Topics will include: * exact cosmological solutions of the Einstein equations * averaging and backreaction in cosmology * numerical cosmological relativity * observational tests