Weyl points and line nodes are three-dimensional linear point-and line-degeneracies between two bands. In contrast to Dirac points, which are their two-dimensional analogues, Weyl points are stable in the momentum space and the associated surface states are predicted to be topologically non-trivial. However, Weyl points are yet to be discovered in nature. Here, we report photonic crystals, based on the double-gyroid structures, exhibiting frequency-isolated Weyl points with intricate phase diagrams. The surface states associated with the non-zero Chern numbers are demonstrated. Line nodes are also found in similar geometries; the associated surface states are shown to be flat bands. Our results are readily experimentally realizable at both microwave and optical frequencies.Two-dimensional (2D) electrons and photons at the energies and frequencies of Dirac points exhibit extraordinary features [1][2][3][4][5]. As the best example, almost all the remarkable properties of graphene are tied to the massless Dirac fermions at its Fermi level [6,7]. Topologically [8], Dirac cones are not only the critical points for 2D phase transitions but also the unique surface manifestation of a topologically gapped 3D bulk. In a similar way, it is expected that if a material could be found that exhibits a 3D linear dispersion relation, it would also display a wide range of interesting physics phenomena. The associated 3D linear pointdegeneracies are called "Weyl points". In the past year, there have been a few studies of Weyl fermions in electronics [9][10][11][12][13][14]. The associated Fermi-arc surface states, quantumHall-effect [15], novel transport properties [16] and the realization of the Adler-Bell-Jackiw anomaly [17] are also expected. However, no observation of Weyl points has been reported. Here, we present a theoretical discovery and detailed numerical investigation of frequency-isolated Weyl points in perturbed double-gyroid(DG) photonic crystals(PhCs) along with their complete phase diagrams and their topologicallyprotected surface states. PhCs containing frequency-isolated linear line-degeneracies, known as "line nodes", and their flatband surface states are also presented. Unlike the proposed Weyl points in electronic system thus far, our predictions in photonics are readily realizable in experiments.Before proceeding, we first point out one intriguing distinction between the 2D Dirac points and the 3D Weyl points. 2D Dirac cones are not robust; they are only protected by the product of time-reversal-symmetry(T) and parity(P, inversion). In 2D, Dirac cone effective Hamiltonian takes the form of H(k) = v x k x σ x + v z k z σ z ; this form is protected by PT (product of P and T) which requires H(k) to be real. Thus, one can open a gap in this dispersion relation upon introducing a perturbation proportional to σ y = 0 −i i 0 that is imaginary;for example, even an infinitesimal perturbation that breaks just P or just T will open a gap. In contrast, 3D Weyl points are topologically protected gapless dispersions robust...