Born in 1946, Frans X. Plooij studied in the Netherlands with Adriaan Kortlandt, University of Amsterdam, with Hein Oomen, University of Nijmegen, and with Gerard Baerends, University of Groningen, where he received his Ph.D. in 1980.In 1971-73, he and his wife Hetty van de Rijt worked with Jane Goodall in the Gombe National Park, Tanzania, East-Africa, on infant development in free-living chimpanzees. In 1973-76 he worked with Robert Hinde in the Medical Research Council unit on the Development and Integration of Behaviour, University Sub-department of Animal Behaviour in Madingley, Cambridge, England; in 1976-80 at the department of Developmental Psychology, University of Nijmegen, the Netherlands; and from 1981 to 1993 as head of the department of Research and Development at the institute for Child Studies of the City of Amsterdam, the Netherlands, where, among other things, he participated in European Union SOCRATES-LINGUA projects concerning the implementation of an innovative second- and foreign-language teaching method for small schoolchildren.From 1993 to 1998, he was a professor at the Department of Developmental and Experimental Clinical Psychology, University of Groningen.He is currently president of the International Research-institute on Infant Studies (IRIS) at Arnhem, the Netherlands, initiator of the European project on "the intercultural study of infantile regression periods" (ISIRP), and director of Kiddy World Promotions B.V., a consulting firm that serves companies producing products related to children, such as toys.Dr. Plooij was Vice-president for Information of the International Society for Human Ethology from 1989-1993, Vice-president of the Institut Européen pour le Development de tous les Enfants (IEDPE), served on the editorial board of the journal "Ethology and Sociobiology", and was member of the panel of assessors of the Journal of Clinical Child Psychology and Psychiatry.He is a full member of several international, scientific societies in the domains of child development and behavioural biology, and of the New York Academy of Sciences.In addition to numerous scientific publications, Dr. Plooij has written several best-selling parenting books, one of which, The Wonder Weeks, has been published in many languages, from the USA to Japan. The Wonder Weeks became a Worldwide bestseller on infant development and has sold over 1.5 million copies!