We report the discovery of a 50,000-y-old Neandertal tar-hafted flint tool found off the present-day Dutch coastline. The production of birch tar adhesives was a major technological development, demonstrating complex Neandertal technology and advanced cognitive ability. The rarity of Middle Paleolithic adhesive finds makes each new discovery crucial for improving our understanding of Neandertal lifeways. We demonstrate that birch tar was a routine part of the Neandertal technological repertoire. In addition, the complex know-how required for adhesive production in northwestern Europe during Marine Isotope Stage 4 and 3 was maintained in small groups leading highly mobile lives. This suggests a degree of task specialization and supports the hypothesis that ecological risk drives the development of complex technology.We report the discovery of a 50,000-y-old birch tar-hafted flint tool found off the present-day coastline of The Netherlands. The production of adhesives and multicomponent tools is considered complex technology and has a prominent place in discussions about the evolution of human behavior. This find provides evidence on the technological capabilities of Neandertals and illuminates the currently debated conditions under which these technologies could be maintained. 14C-accelerator mass spectrometry dating and the geological provenance of the artifact firmly associates it with a host of Middle Paleolithic stone tools and a Neandertal fossil. The find was analyzed using pyrolysis-gas chromatography-mass spectrometry, X-ray micro-computed tomography, and optical light microscopy. The object is a piece of birch tar, encompassing one-third of a flint flake. This find is from northwestern Europe and complements a small set of well-dated and chemically identified adhesives from Middle Paleolithic/Middle Stone Age contexts. Together with data from experiments and other Middle Paleolithic adhesives, it demonstrates that Neandertals mastered complex adhesive production strategies and composite tool use at the ...