The present invention relates to certain phenyl-urea and phenyl-carbamate derivatives comprising a bicyclic heteroaryl group, pharmaceutical compositions containing them, and methods of using them, including methods for preventing, reversing, slowing, or inhibiting protein aggregation, and methods of treating diseases that are associated with protein aggregation, including neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, Lewy body disease, and multiple system atrophy.