His celebrated books/videos -Happiest Baby on the Block, Happiest Toddler on the Block and Happiest Baby Guide to Great Sleep: Birth to Five – have been used by millions of parents. Dr. Karp’s landmark theories have helped explain and mitigate some of the most stressful new parent challenges, like infant crying, poor sleep and toddler tantrums. Thousands of certified Happiest Baby educators teach his work in hospitals and clinics across America and 20 other nations. For over 20 years, Dr. Karp has also been an advocate for children’s environmental health. He helped found Healthy Child Healthy World and serves on the board of the Environmental Working Group.