The defining problem in frustrated quantum magnetism, the ground state of the nearest-neighbor S ¼ 1=2 antiferromagnetic Heisenberg model on the kagome lattice, has defied all theoretical and numerical methods employed to date. We apply the formalism of tensor-network states, specifically the method of projected entangled simplex states, which combines infinite system size with a correct accounting for multipartite entanglement. By studying the ground-state energy, the finite magnetic order appearing at finite tensor bond dimensions, and the effects of a next-nearest-neighbor coupling, we demonstrate that the ground state is a gapless spin liquid. We discuss the comparison with other numerical studies and the physical interpretation of this result. DOI: 10.1103/PhysRevLett.118.137202 In one spatial dimension (1D), quantum fluctuations dominate any physical system and semiclassical order is destroyed. In higher dimensions, frustrated quantum magnets offer perhaps the cleanest systems for seeking the same physics, including quantum spin-liquid states, fractionalized spin degrees of freedom, and exotic topological properties. This challenge has now become a central focus of efforts spanning theory, numerics, experiment, and materials synthesis [1][2][3][4]. While much has been understood about frustrated systems on the triangular, pyrochlore, Shastry-Sutherland, and other 2D and 3D lattices, it is fair to say that the ground-state properties of the S ¼ 1=2 kagome Heisenberg antiferromagnet (KHAF) remain a complete enigma.An analytical Schwinger-boson approach [5], coupledcluster methods [6], and density-matrix renormalizationgroup (DMRG) calculations [7][8][9], including analysis of the topological entanglement entropy [10], all suggest a gapped spin liquid of Z 2 topology. The most sophisticated DMRG studies [9,11] estimate a triplet spin gap Δ ≥ 0.05J. Analytical large-N expansions [12] and numerical simulations by the variational Monte Carlo (VMC) technique [13,14] suggest a gapless spin liquid with U(1) symmetry and a Dirac spectrum of spinons. Extensive exactdiagonalization calculations conclude that the accessible system sizes are simply too small to judge [15,16]. Debate continues between the gapped Z 2 and gapless U(1) scenarios, with very recent arguments in support of both [17,18], while a study using symmetry-preserving tensor-network states (TNS) favors the gapped Z 2 ground state [19]. Experimental approaches to the kagome conundrum have made considerable progress in recent years, but for the purposes of the current theoretical analysis we defer a review to Sec. SI of the Supplemental Material (SM) [20].In this Letter, we employ the projected entangled simplex states (PESS) description of the entangled many-body ground state to compute the properties of the KHAF. Because we consider an infinite system, our results provide hitherto unavailable insight. As functions of the finite tensor bond dimension, we find algebraic convergence of the ground-state energy and algebraic vanishing of a finite stagger...