We investigate the locality of interactions in hydrodynamic turbulence using data from a direct numerical simulation on a grid of 1024 3 points; the flow is forced with the Taylor-Green vortex. An inertial range for the energy is obtained in which the flux is constant and the spectrum follows an approximate Kolmogorov law. Nonlinear triadic interactions are dominated by their non-local components, involving widely separated scales. The resulting nonlinear transfer itself is local at each scale but the step in the energy cascade is independent of that scale and directly related to the integral scale of the flow. Interactions with large scales represent 20% of the total energy flux. Possible explanations for the deviation from self-similar models, the link between these findings and intermittency, and their consequences for modeling of turbulent flows are briefly discussed.PACS numbers: 47.27. Eq,47.27.Ak,47.65.+a Flows in nature are often in a turbulent state driven by large scale forcing (e.g. novae explosions in the interstellar medium) or by instabilities (e.g. convection in the sun). Such flows involve a huge number of coupled modes leading to great complexity both in their temporal dynamics and in the physical structures that emerge. Many scales are excited, for example from the planetary scale to the kilometer for convective clouds in the atmosphere, and much smaller scales when considering microprocesses such as droplet formation. The question then arises concerning the nature of the interactions between such scales: are they predominantly local, involving only eddies of similar size, or are they as well non-local? It is usually assumed that the dominant mode of interaction is the former, and this hypothesis is classically viewed as underlying the Kolmogorov phenomenology that leads to the prediction of a E(k) ∼ k −5/3 energy spectrum; such a spectrum has been observed in a variety of contexts although there may be small corrections to this power-law due to the presence in the small scales of strong localized structures, such as vortex filaments [1].Several studies have been devoted to assess the degree of locality of nonlinear interactions, either through modeling of turbulent flows, as is the case with rapid distortion theory (RDT) [2] or Large Eddy Simulations (LES) [3], or through the analysis of direct numerical simulations (DNS) of the Navier-Stokes equations (see e.g. [3, 4, 5]), and more recently through rigorous bounds [6]. The spatial resolution in the numerical investigations was moderate, without a clearly defined inertial range and the differentiation between local and non-local interactions was somewhat limited. Thus, a renewed analysis at substantially higher Reynolds numbers in the absence of any modeling is in order; we address this issue by analyzing data stemming from a newly performed DNS on a grid of 1024 3 points using periodic boundary conditions.The governing Navier-Stokes equation for an incompressible velocity field v, with P the pressure, F a forcing term and ν = 3 × 10 −4 the...