OpenQSEI: A MATLAB package for quasi static elasticity imaging. Quasi Static Elasticity Imaging (QSEI) aims to computationally reconstruct the inhomogeneous distribution of the elastic modulus using a measured displacement field. QSEI is a well-established imaging modality used in medical imaging for localizing tissue abnormalities. More recently, QSEI has shown promise in applications of structural health monitoring and materials characterization. Despite the growing usage of QSEI in multiple fields, fully-executable open source packages are not readily available. To address this, OpenQSEI is developed using a MATLAB platform and shared in an online community setting for continual algorithmic improvement. In this article, we describe the mathematical background of QSEI and demonstrate the basic functionalities of OpenQSEI with examples.