Born in 1944, Hetty van de Rijt-Plooij studied Educational Psychology at the University of Nijmegen, the Netherlands and worked following graduation in an institute for the mentally handicapped. From 1971 to 1973, with her husband Frans Plooij, she studied infant development in free-living chimpanzees with Dr. Jane Goodall in the Gombe National Park, Tanzania, East Africa. From 1973 to 1976, she studied with Prof. Robert Hinde in the Medical Research Council unit on the Development and Integration of Behaviour. In 1976 her daughter Xaviera was born. She obtained her Ph.D. in Physical Anthropology at the University of Cambridge, England in 1982.

As a researcher at the University of Amsterdam, the Netherlands from 1986 to 1990, she studied the development of human babies in their home environment through direct observations, filming, and in-depth interviews with their parents.

As lead author with her husband as co-author, she wrote the best-selling parenting book The Wonder Weeks, which has been published in twelve languages, from the USA to Japan. She designed a parental support and education program called Leaping hurdles, based on the Wonder Weeks and published a scientific evaluation study to report on the results of this program. She died far too young at the age of 59.