The Association Montessori Internationale (AMI) - the original organization to promote the ideas and principles of Maria Montessori; trains teachers and accredits schools.      
The North American Montessori Teacher's Association (NAMTA) - a resource of information about Montessori education, for parents, teachers, and administrators.
Montessori Online - The online resource center provided by the Montessori Foundation
and the International Montessori Council.
National Catholic Educators Association (NCEA) - The professional association for all Catholic educators is a voluntary association of educators and institutions. Individual and affiliate memberships represent Catholic education at all levels and in a variety of settings: preschools, elementary, and secondary schools, parish catechetical/religious education programs, diocesan offices, colleges, universities and seminaries.
Montessori Services - A Resource for Preparing the Child's Environment.
Michael Olaf - An introduction to Montessori philosophy in all its aspects.