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An important starting point on research on humanism are the following handbooks:

The Oxford Handbook of Humanism

https://global.oup.com/academic/product/the-oxford-handbook-of-humanism-9780190921538?

The Oxford Handbook of Secularism

https://global.oup.com/academic/product/the-oxford-handbook-of-secularism-9780199988457?cc=at&lang=en&

The Wiley Blackwell Handbook of Humanism

https://onlinelibrary.wiley.com/doi/book/10.1002/9781118793305