Chasm is a toolkit providing seamless language interoperability between Fortran 95 and C++. Language interoperability is important to scientific programmers because scientific applications are predominantly written in Fortran, while software tools are mostly written in C++. Two design features differentiate Chasm from other related tools. First, we avoid the common-denominator type systems and programming models found in most Interface Definition Language (IDL)-based interoperability systems. Chasm uses the intermediate representation generated by a compiler front-end for each supported language as its source of interface information instead of an IDL. Second, bridging code is generated for each pairwise language binding, removing the need for a common intermediate data representation and multiple levels of indirection between the caller and callee. These features make Chasm a simple system that performs well, requires minimal user intervention and, in most instances, bridging code generation can be performed automatically. Chasm is also easily extensible and highly portable.