OOMPAA -- Object-oriented model for probing assemblages of atoms. An object-oriented library is presented for building molecular-modeling software. This library allows the user to treat individual components of molecules as C++ objects, and provides various templated lists and vector classes for manipulating these objects. Other utilities, such as minimizers and integrators, are continually being added to the body of code. Performance is a key consideration; the performance of simple benchmarks is comparable to that of hand-coded Fortran.