Focal cortical dysplasia (FCD) is one of the most important causes of drug-resistant epilepsy in paediatric patients, particularly in those below the age of 3. Even though over 40 years have passed since the first description of the entity by Taylor, the exact mechanisms causing these cortical abnormalities remain unelucidated. In this review, we summarise the current knowledge on clinical and histopathological aspects, taking into account the new classification system proposed by the International League Against Epilepsy. We focus on the clinicopathological associations and differences in post-surgical outcome among FCD subtypes, in particular isolated FCD vs. FCD associated with principal lesions, which have not been summarised to date. We also recapitulate genetic studies, pointing to the possible mechanisms of the cortical dysregulation and drug resistance, and summarise novel factors which may contribute to epileptogenesis in FCD. Furthermore, we compare FCD type IIB (FCDIIB) with brain tumours found in a neurocutaneous disorder, tuberous sclerosis, as we evaluate the hypothesis that FCD IIB may be a local form of this disease.