Since 1994 Hellemans has contributed more than 100 articles to Science Magazine (AAAS, Washington), writing about developments in physics, astronomy, and science policy. He contributes regularly to Physics World and is a Contributing Editor for IEEE Spectrum Magazine. He has published articles in Nature, Scientific American, The Guardian (UK), The New Scientist, The Scientist, The Independent (UK), Astronomy (Waukesha, WI), Sky & Telescope (Cambridge, MA), Europhysics News (France), The Industrial Physicist (AIP, Washington), Physikalische Blaetter (Germany), Natuur en Techniek (The Netherlands), NRC-Handelsblad (The Netherlands), De Standaard (Belgium), and La Recherche (France). He has been the guest editor for the special issues on science and technology of Publishers Weekly (New York) from 1983 to 1987.
With Bryan Bunch, Hellemans is the author of The History of Science and Technology: A Browser's Guide to the Great Discoveries, Inventions, and the People Who Made Them from the Dawn of Time to Today, published by Houghton-Mifflin (Boston) in April 2004. Previously both authors published The Timetables of Science (1988) and The Timetables of Technology (1993), published by Simon and Schuster in New York. Both books are reprinted as Touchstone paperbacks. The Timetables of Science has also been published in the UK, Germany, Japan, and Romania.
From 1984 to 1987 Hellemans was the book review editor at Physics Today (AIP). He has also worked as an editor and writer for several encyclopedias and yearbooks, including the McGraw-Hill Encyclopedia of Science and Technology and the World Book Encyclopedia. Hellemans is a Belgian national and fluent in English, French, German, Dutch and Italian.