Questioning is widely recognised as a key dimension of learning in science education, yet learner questioning has often been treated as a secondary aspect of classroom participation rather than as a central pedagogical and epistemic practice. This article offers a conceptual examination of questioning in relation to science education for sustainability, informed by a critical interpretive engagement with literature on questioning, participation, classroom dialogue, engagement, and science education. It argues that science education for sustainability requires more than the transmission of scientific knowledge, calling instead for pedagogical spaces in which learners can engage with complexity, uncertainty, interpretation, and the ethical and social dimensions of socio-scientific issues. The article’s main contribution lies in repositioning learner questioning as a central condition of science education for sustainability and in showing that questioning is shaped not only by knowledge and motivation, but also by participation, hesitation, silence, and broader dynamics of voice, legitimacy, and power. In this perspective, fostering questioning becomes essential to more inclusive, dialogic, reflexive, and transformative approaches to science education for sustainability. The article further argues that fostering questioning in this way contributes directly to the educational ambitions embedded in SDG 4, SDG 13, and SDG 16 - making questioning-centred pedagogy not merely a methodological choice, but a condition for more democratic, just, and transformative science education for sustainable development.