The Philosophy and Practice of the Montessori Method of Education
www.michaelolaf.net

American Montessori Society: 

AMS provides the leadership and inspiration to make Montessori a significant voice in education.  The Society advocates quality Montessori education, strengthens members through its services, and champions Montessori principles to the greater community.
www.amshq.org

The Montessori Foundation

The Montessori Foundation is a nonprofit organization dedicated to the advancement of Montessori education in the United States and abroad.
www.montessori.org

Canadian Council of Montessori Administrators
www.ccma.ca/ccma/montessori.html

Tomorrow's Child
www.tomorrowschildmi.org/