The theoretical foundations for DIGICOMPASS Junior build on the original DIGICOMPASS framework, adapting core ideas to the cognitive, social, emotional, and linguistic needs of upper primary learners while staying true to its vision of global, inclusive language education. The chapter anchors practice in Constructivism, Sociocultural Theory, Self-Determination Theory, Connectivism, and Cognitive Load Theory, read through a non-deterministic view of development and an ecological lens on context. These anchors are operationalized through design principles: multimodal learning, cognitive load awareness (enacting CLT), plurilingualism/translanguaging and funds of knowledge, reflection, and metacognition. Together, they support active exploration, scaffolded thinking, identity-affirming participation, sustained motivation, and safe digital connectedness. The result is a coherent, developmentally realistic approach that helps learners communicate across languages and cultures and helps teachers translate theory into day-to-day routines and tasks.