ARRL's Logbook of the World (LoTW) system is a repository of log records submitted by users from around the world. When both participants in a QSO submit matching QSO records to LoTW, the result is a QSL that can be used for ARRL award credit.
To minimize the chance of fraudulent submissions to LoTW, all QSO records must be digitally signed using a digital certificate obtained from ARRL. Obtaining such a certificate requires verification of the licensee's identity either through mail verification (US) or inspection by ARRL of required documentation (non-US).
Software developed by ARRL can be used to convert a log file (in ADIF or Cabrillo file format) into a file of digitally signed QSO data, ready for submission to LoTW.
LoTW began operation on September 15, 2003.