WRRmod 2024 is the 9th IWA Water Resource Recovery Modelling Seminar of the biennial modelling seminar series. The WRRmod conference connects academics, engineering experts, and scientists specializing in modelling wastewater treatment processes. The seminar provides a platform for sharing ideas regarding the most recent innovative research and practices together with future prospects in modelling water resource recovery facilities (WRRF). A cornerstone of WRRmod is the facilitation of engagement on changing paradigms and globally relevant topics in this area of specialization and the building of consensus amongst the community of WRRF modellers.  A focus of WRRmod 2024 will the discussion and advancement of best practices for the application of WRRF models to solve some of our most challenging environmental problems, including decarbonization, operational efficiency, nutrient removal, biosolids reuse, and watershed solutions.