Subsidiarity is one of Catholic social teaching’s key concepts. I included a whole chapter on it in my book, Faith Meets World. Today at Crux, Robert Christian offers a helpful and clear explanation of subsidiarity. He provides a clear definition and also notes what it’s not (there are some bad definititions out there about it), notes how respect for it protects us and enriches our lives, and briefly points out where we see it and rejections of it at work in history and the present day. All in all, worth a look! You can find it here.