Renewable energy conversion and storage play an important role in our global efforts to limit the drastic effects of climate change. In particular, the electrocatalytic reduction of carbon dioxide to chemicals and fuels can bring us closer towards a closed-loop anthropogenic carbon cycle. Significant breakthroughs are often the result of deeper understandings of reaction mechanisms, material structures and surface sites. To this end, operando techniques have been invaluable in combining advanced characterization of a catalyst with simultaneous measurements of its activity and selectivity under real working conditions. This Review aims to highlight significant progress in the use of operando characterization techniques that enhance our understanding of heterogeneous electrocatalytic CO₂ reduction. We provide a summary of the most recent mechanistic understanding using operando optical, X-ray and electron-based techniques, along with key questions that need to be addressed. We conclude by offering some insight on emerging directions and prospects in the field.