A Double-Double and Quad-Double Arithmetic library. Double-double and quad-double numbers are unevaluated sum of two and four IEEE doubles capable of representing 106 and 212 bits of significand, respectively. The library is written in C++, taking full advantage of operator overloading. C, Fortran 77, and Fortran 90 interfaces are also provided. This work was done at Lawrence Berkeley National Laboratory, NERSC Division, Yozo Hida with Xiaoye S. Li and David H. Bailey.