In this contribution, we present ddX, an open-source implementation of ddCOSMO, ddPCM, and ddLPB that comes with clear APIs and is designed to be easily interfaced with both classical and quantum descriptions. We believe that the ddX library, besides being the coronation of more than ten years of methodological developments, can provide both quantum chemists and biophysicists with a unified tool to treat solvation effects with a polarizable model. It can be used consistently for any application, ranging from the simulation of electronic spectra to molecular dynamics, from quantum mechanical geometry optimizations to the calculation of the electrostatic solvation energy of large biomolecules. The library is distributed on GitHub () under the permissive LGPL v3 license and has been provided with an automatically generated documentation, available at . So far we have interfaced ddX both with codes from quantum chemistry (Psi4 70 and adcc 71 ) as well as classical MD simulation (Tinker ), which will be demonstrated below. This paper is organized as follows: in Sec. 2 we introduce the models available in ddX and give a brief overview on the computation of energy and the analytical derivatives. In Sec. 3, we present the layout of the implementation of the ddX library along with some details about the fast multipole method (FMM) and our code design. In Sec. 4, we present our interface to Tinker, Psi4 and adcc in detail. Lastly, in Sec. 5, we test the ddX library on molecules with atoms up to 10 5 atoms. The supporting information provides the finer details about the matrix formulation for the models.