We consider pure quantum states of N qubits and study the genuine N −qubit entanglement that is shared among all the N qubits. We introduce an information-theoretic measure of genuine N -qubit entanglement based on bipartite partitions. When N is an even number, this measure is presented in a simple formula, which depends only on the purities of the partially reduced density matrices. It can be easily computed theoretically and measured experimentally. When N is an odd number, the measure can also be obtained in principle.PACS numbers: 03.67.-a, 03.65. Ud, 73.43.Nq, 89.70.+c The nature of quantum entanglement is a fascinating topic in quantum mechanics since the famous EinsteinPodolsky-Rosen paper [1] in 1935. Recently, much interest has been focused on entanglement in quantum systems containing a large number of particles. On one hand, multipartite entanglement is valuable physical resource in large-scale quantum information processing [2,3]. On the other hand, multipartite entanglement seems to play an important role in condensed matter physics [4], such as quantum phase transitions (QPT) [5,6] and high temperature superconductivity [7]. Therefore, how to characterize and quantify multipartite entanglement remains one of the central issues in quantum information theory.In the present literature, there exist very few measures of multipartite entanglement with a clear physical meaning [8,9,10,11,12,13,14,15]. Because of this, most research in quantum entanglement and QPT focused on bipartite entanglement, for which there have been several well defined measures [16,17,18,19,20,21,22]. However, bipartite entanglement can not characterize the global quantum correlations among all parties in a multiparticle system. Since the correlation length diverges at the critical points, multipartite entanglement plays an essential role in QPT. Though localizable entanglement (LE) [23] can be used to describe long-range quantum correlations, its determination is a formidable task for generic pure states. Therefore, computable measure of multipartite entanglement with clear physical meanings are highly desired [24,25].In this paper, we define a new measure of genuine N −qubit entanglement based on different bipartite partitions of the qubits and existing measures for mutual information. The central idea is that, through bipartite partitions, we can get information about the genuine multi-qubit entanglement. Our measure is a polynomial SLOCC (stochastic local operations and classical communication) invariant [26] and is unchanged under permutations of qubits. When N is an even number, we derive * Electronic address: zwzhou@ustc.edu.cn a simple formula for this measure, which is determined by the purity of partially reduced density matrices only. It can be computed through experimentally observable quantities [10,27]. Therefore, it is easy to obtain not only theoretically but also experimentally. For N = 4, we show that this measure satisfies all the necessary conditions required for a natural entanglement measure [20] exactly....