In this paper, we propose a general framework for tensor singular value decomposition (tensor SVD), which focuses on the methodology and theory for extracting the hidden lowrank structure from high-dimensional tensor data. Comprehensive results are developed on both the statistical and computational limits for tensor SVD. This problem exhibits three different phases according to the signal-to-noise ratio (SNR). In particular, with strong SNR, we show that the classical higher-order orthogonal iteration achieves the minimax optimal rate of convergence in estimation; with weak SNR, the information-theoretical lower bound implies that it is impossible to have consistent estimation in general; with moderate SNR, we show that the non-convex maximum likelihood estimation provides optimal solution, but with NP-hard computational cost; moreover, under the hardness hypothesis of hypergraphic planted clique detection, there are no polynomial-time algorithms performing consistently in general.[28] may yield sub-optimal result. We will further illustrate this phenomenon by numerical analysis in Section 5.Remark 2. Especially when r = 1, Theorem 1 confirms the heuristic conjecture raised in Richard and Montanari [23] that the tensor unfolding method yields reliable estimates for order-3 spiked tensors provided that λ/σ > O(p 3/4 ). Moreover, Theorem 1 further shows the power iterations are necessary in order to refine the reliable estimates to minimax-optimal estimates. Our result in Theorem 1 outperforms the ones by Sum-of-Squares (SOS) scheme (see, e.g., [24,36]), where an additional logarithm factor on the assumption of λ is required. In addition, the method we analyze here, i.e., HOOI, is efficient, easy to implement, and achieves optimal rate of convergence for estimation error.Remark 3. The strong SNR assumption (λ/σ ≥ Cp 3/4 ) is crucial to guarantee the performance of Algorithm 1. Actually, to ensure that Step 1 in Algorithm 1 provides meaningful initializations, λ should be at least of order p 3/4 according to our theoretical analysis.Moreover, the estimators with high likelihood, such as MLE, achieve the following upper bounds under weaker assumption that λ/σ ≥ Cp 1/2 .