libuninum is a library for converting Unicode strings to integers and integers to Unicode strings. Internal computation is done using arbitrary precision arithmetic, so there is no limit on the size of the integer that can be converted. Values are passed and returned as ASCII decimal strings, GNU MP mpz_t objects, or unsigned long integers. Auto-detection of the number system is provided. Very many number systems are supported. Group delimitation for output strings is fully controllable. Command line and graphical interfaces are also provided.