We propose a new finite sample corrected variance estimator for the linear generalized method of moments (GMM) including the one-step, two-step, and iterated estimators. Our formula additionally corrects for the over-identification bias in variance estimation on top of the commonly used finite sample correction of Windmeijer (2005) which corrects for the bias from estimating the efficient weight matrix, so is doubly corrected. Formal stochastic expansions are derived to show the proposed double correction estimates the variance of some higher-order terms in the expansion. In addition, the proposed double correction provides robustness to misspecification of the moment condition. In contrast, the conventional variance estimator and the Windmeijer correction are inconsistent under misspecification. That is, the proposed double correction formula provides a convenient way to obtain improved inference under correct specification and robustness against misspecification at the same time.1 two-step linear GMM. Specifically, his formula corrects for the bias arising from using the efficient weight matrix being evaluated at an estimate, rather than the true value. The correction formula (the Windmeijer correction, hereinafter) has been routinely used in practice. 1 However, the Windmeijer correction does not take into account for the over-identification bias, which is another important source of bias in the GMM standard error. The over-identification bias arises from the fact that the over-identified sample moment condition is nonzero while it converges in probability to zero under correct specification.We propose a new finite sample correction which takes into account for the over-identification bias for the variance of the linear one-step, two-step, and iterated GMM estimators. For one-step GMM such as the two-stage least squares (2SLS) estimators, the proposed finite sample correction is new as the Windmeijer correction does not cover the one-step GMM. For two-step and iterated GMM, the proposed correction improves upon the Windmeijer correction by additionally correcting for the over-identification bias. Thus, we doubly correct the finite sample bias of the linear GMM variance estimator. We provide an additional formal justification of the proposed double correction by deriving the stochastic expansions of the GMM estimators under local misspecification where the moment condition is modeled as a local drifting sequence around zero. The result shows that the double correction estimates the (co)variance of some higher-order terms which increase with the overidentification bias. Rothenberg (1984) provides a general treatment of the stochastic expansion and Newey and Smith (2004) derive the stochastic expansion of GMM and the generalized empirical likelihood (GEL) estimators under correct specification. The order of our double correction equals the order of the sample moment condition. Under correct specification or local misspecification, these terms are O p (n −1/2 ) so that the double correction is a finite-sample corr...