Online Resources
A plethora of Montessori websites are available. Here are some of my favorite:
Recommended Books
Some of the very best books are, of course, out of print, so if you can find them somewhere, The Advanced Montessori, Volumes 1 & 2 are very instructive. As a general rule, anything written by Maria Montessori is a worthwhile read. Paula Polk Lillard is also a very good Montessori author, and the book shown above is her best as far as I am concerned.