‘Trans-Atlantic slave trade by Mennonites in Amsterdam, 1655-1674, and the erosion of the principle of defencelessness’ In the period 1655-1674 the first West-Indian Company (1621-1674) gave permission to private shipowners in Amsterdam, on payment of a tax, for private slave trade with West-Africa. This article concerns thirteen of the 270 shipowners who made use of this possibility. They were members of Mennonite churches and participated as copartners in eleven of the 135 privately-owned slave ships. A fourteenth Mennonite member served as a supercargo on shipboard to sell the slaves in the West Indies. As Mennonite Amsterdam made up 3,5 percent of the population, these fourteen members provided a pro rata contribution to the private slave trade of this period in this city. Each description of a slave ship with a Mennonite participator is introduced by information on his or her social and financial background and other commercial enterprises. The Mennonite principle of defencelessness was neglected without protest of the Mennonite churches. This corresponds with the increasing erosion of the principle which culminated in the year 1672 when the Mennonite churches lent enormous amounts of money to the Dutch State for the defense of the country.