Published by the American Geophysical Union as part of the Special Publications Series. No one would dispute that 1985 and 1986 were unique times for cometary research. In September 1985 ISEE-3 transited the magnetotail of comet Giacobini-Zinner and provided the first close-up scientific view of a cometary environment. Half a year later an international fleet of spacecraft equipped with state-of-the-art instrumentation gave us a “once-in-a-lifetime” look at comet Halley.