PhilPapers is a comprehensive index of philosophy books and articles. PhilPapers offers unique features such as real-time indexing of pre-prints, fine-grained classification by topic, email alerts, reading lists, advanced search functionality, and discussion forums. PhilPapers' index and its archive are integrated with the largest structured bibliography in the field. PhilPapers' structured bibliography organizes half a million entries into 5,069 topics at different levels of generality. Classification is maintained by a combination of automatic classification, crowd-sourcing, and curation work done by approximately 400 appointed academics.