International Ocean Discovery Program (IODP) Expedition 387 is based on IODP drilling proposal Number 859-Full2 and 859-Add2 (http://iodp.tamu.edu/scienceops/expeditions/amazon_margin.html). Following evaluation by the IODP Scientific Advisory Structure, the expedition was scheduled for the R/V JOIDES Resolution, operating under contract with the JOIDES Resolution Science Operator (JRSO).At the time of publication of this Scientific Prospectus, the expedition is scheduled to start in Georgetown, Barbados, on 26 April 2020 and end in Fortaleza, Brazil, on 26 June 2020. A total of 61 days will be available for the initial port call, transit, drilling, coring, and downhole measurements described in this report. For the current detailed schedule, see http://iodp.tamu.edu/scienceops. Further details about the facilities on board JOIDES Resolution can be found at http://iodp.tamu.edu/publicinfo/drillship.html.