Coulomb interactions between electrons on neighboring chains and one-electron interchain tunneling lead to coupling of the fluctuations on neighboring chains. Experimental evidence for fluctuation effects has been found in a variety of materials in which charge or spin density wave ground states occur at low temperatures. The progressive development of density wave fluctuations is accompanied by corresponding changes in the phonon and electron densities of states. The fluctuations of the charge density wave order parameter can be examined by X-ray or neutron scattering. Due to interchain interactions density wave fluctuations on the neighboring chains become correlated and this leads to a transition to a ground state with three-dimensional, long range order. Fluctuation effects lead to pronounced changes in the density of single particle electron states, and the gradual opening of the pseudogap has been inferred from the magnetic susceptibility and optical properties.