The intbitset library provides a set implementation to store sorted unsigned integers either 32-bits integers or an infinite range with fast set operations implemented via bit vectors in a Python C extension for speed and reduced memory usage. The inbitset class emulates the Python built-in set class interface with some additional specific methods such as its own fast dump and load marshalling functions. intbitset additionally support the pickle protocol, the iterator protocol and can behave like a sequence that can be sliced. Because the integers are always stored sorted, the first element of a non-empty set [0] is also the min() integer and the last element [-1] is also the max() integer in the set. When compared to the standard library set class, intbitset set operations such as intersection, union and difference can be up to 5000 faster for dense integer sets.