We demonstrate that a soft substrate of a stiffness that matches the embryonic stem cell stiffness can promote homogenous self-renewal and pluripotency of these cells, even in the absence of the growth factor-Leukemia Inhibitory Factor (LIF). These findings open the field of stem cell biology for long term culture of embryonic stem cells without generating a heterogeneous population of cells with varying degrees of differentiation and highlight the importance of mechanics in dictating embryonic stem cell pluripotency. To read the abstract and the paper, see http://dx.plos.org/10.1371/journal.pone.0015655