The authors describe a 3-year project to design and test a multilingual literacy curriculum that centers language and student voice in the service of literacy development for multilingual learners. In the first 2 years, researchers, teachers, and students worked together to develop the curriculum using design-based, case study methods. In the third year, teachers participated in a quasi-experimental implementation of the curriculum that showed positive effects on students' language, reading, and writing outcomes. This longitudinal work reflects four broad principles for multilingual literacy instruction: (1) focus on language and metalinguistic awareness; (2) enact dialogic approaches to engage students; (3) use multimodal texts and scaffolds to support comprehension and expression; and (4) take a multilingual perspective. The authors provide an overview of the curriculum design process and the quasi-experimental field trial. Then, each principle is theoretically and empirically unpacked, and instructionally described using qualitative data collected over the full 3 years.