This report contains the findings from a rapid biological assessment of the Grensgebergte and Kasikasima mountains of southeastern Suriname. Suriname is one of the last places on Earth where an opportunity still exists to conserve huge tracts of pristine, diverse tropical forests. This volume is part of a series of surveys in Suriname designed to support the protection of biodiversity and freshwater and other ecosystem services through collection of baseline biological and socioeconomic data. The researchers in southeastern Suriname investigated plants, mammals, birds, reptiles, amphibians, fishes, insects, and water quality. Over one hundred new species were discovered, including fish, beetles, and katydids.