Seizures are common in the neonatal period, affecting 1 to 3 per 1000 births, and are responsible for significant neurodevelopmental impairment. Etiologies of seizures in neonates can be broadly classified into acute provoked seizures and neonatal-onset epilepsies. The most common cause of acute seizures in neonates is hypoxic-ischemic encephalopathy, where a reduced flow of oxygenated blood to the brain before or during delivery leads to brain dysfunction. Other causes of acute seizures are stroke, infection, or acute electrolyte and glucose imbalances. On the other end of the spectrum, neonatal-onset epilepsies are a large group of rare and ultra-rare diseases. Early recognition of the etiology-specific electro-clinical phenotypes is essential for targeted treatment. This thesis advanced the field of seizures in neonates by analyzing how EEG background can inform subsequent seizure risk and by performing detailed electroclinical phenotyping of neonates with early-onset genetic epilepsies such as channelopathies and BRAT1 pathogenic variants. (MED - Sciences médicales) -- UCL, 2022