The ETC16 conference, titled “Language and Social Interaction in Heterogeneous Mathematics Classrooms,” took place at Martin Luther University in Halle, Germany, in 2024. This event marked the fourth topic conference of the Mathematics and Language Thematic Working Group (TWG) of ERME, following previous conferences in Dresden, Germany (ETC4, 2018), Montpellier, France (ETC7, 2020), and Oxford, UK (ETC12, 2022). These conferences consistently attract researchers from the ERME community and beyond who are dedicated to exploring various dimensions of language in mathematics education. Key areas of focus include, but are not limited to, interaction processes, multilingualism and language as a resource for teaching and learning, the development of academic language, and classroom discursive practices.