Database website of more than 800.000 images from 133 collections of 100 art organizations in the Netherlands.
Documentation
Pages

Historie in perspectief
Item on graphic New Babylon work that was donated to the town of Meppel in 1967 which was eventually lost.

J. Seegers
Extensive background information about the Situationist International and Constant in English.

Kunstgeografie.nl
About Amsterdam in the sixties. References Constant, his New Babylon project, artists he worked with and his affiliation with the Provos.