Dan Siegel: https://drdansiegel.com/

Dr. Russell Barkley (ADHD): https://www.russellbarkley.org/

Attention Deficit Disorder Association: www.add.org 

Children and Adults with Attention Deficit Hyperactivity Disorder: www.chadd.org

National Institute of Mental Health: www.nimh.hig.gov 

Nonprofit organization with extra materials on ADHD: www.addresources.org