<![CDATA[21st-century education demands learners who can think critically, communicate, collaborate, and create, yet mathematics instruction in many Indonesian elementary schools remains teacher-centered and disconnected from real-life contexts. This conceptual study examines how 21st-century skills (the 4Cs) can be integrated with the STEAM (Science, Technology, Engineering, Arts, and Mathematics) approach in elementary mathematics learning. A qualitative library research method was used: relevant national and international journal articles, books, and policy documents published between 2008 and 2025 were collected, reduced, and analyzed thematically. The findings show that STEAM provides a natural, project-based context in which mathematical content, such as measurement, geometry, and data, becomes the tool students use to design, build, and communicate solutions to authentic problems, thereby simultaneously developing critical thinking, creativity, collaboration, and communication. Three illustrative STEAM-based mathematics activities are presented along with a mapping between STEAM components and the 4C indicators they foster. The study also identifies challenges in implementation, including teachers' limited STEAM literacy, time and resource constraints, and the need for authentic assessment instruments. It is recommended that teacher training, school facilities, and curriculum flexibility be strengthened to support this integration, and that future studies test its effectiveness empirically in elementary classrooms.]]>
