Compressive sampling (CS) aims at acquiring a signal at a sampling rate that is significantly below the Nyquist rate. Its main idea is that a signal can be decoded from incomplete linear measurements by seeking its sparsity in some domain. Despite the remarkable progress in the theory of CS, little headway has been made in the compressive imaging (CI) camera. In this paper, a three-dimensional compressive sampling (3DCS) approach is proposed to reduce the required sampling rate of the CI camera to a practical level. In 3DCS, a generic three-dimensional sparsity measure (3DSM) is presented, which decodes a video from incomplete samples by exploiting its 3D piecewise smoothness and temporal low-rank property. In addition, an efficient decoding algorithm is developed for this 3DSM with guaranteed convergence. The experimental results show that our 3DCS requires a much lower sampling rate than the existing CS methods without compromising recovery accuracy.