This workshop will bring together experts in galaxy formation simulations and observational astronomy to develop and compare robust “forward modelling” techniques that enable fair comparisons between simulated and observed galaxies. Particular emphasis will be placed on modelling emission of stellar populations and AGNs, including dust absorption combined with other observational effects in the ultraviolet, optical, and infrared regimes. The outcome of the workshop will include open-source tools and a white paper with community-wide recommendations.