Abstract. We present a software library Stxxl, that enables practiceoriented experimentation with huge data sets. Stxxl is an implementation of the C++ standard template library STL for external memory computations. It supports parallel disks, overlapping between I/O and computation, and pipelining technique that can save more than half of the I/Os. Stxxl has already been used for computing minimum spanning trees, connected components, breadth-first search decompositions, constructing suffix arrays, and computing social network analysis metrics.