Nitrous oxide (N₂O) emissions from biological wastewater treatment are a significant but uncertain contributor to sectoral greenhouse gas emissions. Long-term monitoring shows that emissions are dynamic, varying with season, load, and operational conditions and influenced by short-duration, high-intensity events. This presentation consolidates results from continuous liquid-phase N₂O monitoring at multiple wastewater treatment plants, covering mainstream activated sludge as well as high-rate and sidestream nitrogen removal processes. Across monitored sites, observed N₂O emission factors ranged from below 0.2% to above 5% of influent nitrogen load, with variability within individual plants exceeding one order of magnitude. In several cases, 40–60% of total emissions occurred during less than 20% of the monitoring period. Elevated N₂O production was associated with high ammonium oxidation rates, low or rapidly fluctuating dissolved oxygen concentrations, and intermittent aeration regimes, with sidestream processes exhibiting higher emission factors than mainstream treatment. Building on the N₂O Mobile project, cross-validation of liquid-phase and off-gas measurements showed strong agreement, while demonstrating that reliable whole-tank and whole-plant emission estimates require representative tank- or zone-level airflow data. Overall, the results show that effective N₂O baselining and mitigation require continuous, in-situ monitoring capable of resolving short-term process dynamics and system-level aeration behaviour.