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We study the topology of large-scale structure in the Center for Astrophysics Redshift Survey, which now includes ~12,000 galaxies with limiting magnitude m_B_ <= 15.5. The dense sampling and large volume of this survey allow us to compute the topology on smoothing scales from 6 to 20 h^-1^ Mpc; we thus examine the topology of structure in both the "nonlinear" and "linear" regimes. On smoothing scales <= 10 h^-1^ Mpc this sample has 3 times the number of resolution elements of samples examined in previous studies. Isodensity surfaces of the smoothed galaxy density field demonstrate that coherent high-density structures and large voids dominate the galaxy distribution. We compute the genus-threshold density relation for isodensity surfaces of the CfA survey. To quantify phase correlation in these data, we compare the CfA genus with the genus of realizations of Gaussian random fields with the power spectrum measured for the CfA survey. On scales <= 10 h^-1^ Mpc the observed genus amplitude is smaller than random phase (96% confidence level). This decrement reflects the degree of phase coherence in the observed galaxy distribution. In other words the genus amplitude on these scales is not a good measure of the power spectrum slope. On scales greater than 10 h^-1^ Mpc, where the galaxy distribution is roughly in the "linear" regime, the genus amplitude is consistent with the random phase amplitude. The shape of the genus curve reflects the strong coherence in the observed structure; the observed genus curve appears broader than random phase (94% confidence level for smoothing scales <= 10 h^-1^ Mpc) because the topology is spongelike over a very large range of density threshold. This departure from random phase is consistent with a distribution like a filamentary net or "walls with holes." On smoothing scales approaching ~20 h^-1^ Mpc the shape of the CfA genus curve is consistent with random phase. There is very weak evidence for a shift of the genus toward a "bubble-like" topology. To test cosmological models, we compute the genus for mock CfA surveys drawn from large (L ~> 400 h^-1^ Mpc) N-body simulations of three variants of the cold dark matter (CDM) cosmogony. The genus amplitude of the "standard" CDM model ({OMEGA}h = 0.5, b = 1.5) differs from the observations (96% confidence level) on smoothing scales <~ 10 h^-1^ Mpc. An open CDM model ({OMEGA}h = 0.2) and a CDM model with nonzero cosmological constant ({OMEGA}h = 0.24, λ_0_ = 0.6) are consistent with the observed genus amplitude over the full range of smoothing scales. All of these models fail (97% confidence level) to match the broadness of the observed genus curve on smoothing scales <= 10 h^-1^ Mpc.