In April 1963 the first Universal House of Justice was elected, six years after the passing of Shoghi Effendi, by 56 national spiritual assemblies. The date of the election coincided with the completion of the Ten Year Crusade and also with the first centenary anniversary of the public declaration of Baha'u'llah in the Garden of Ridvan in April 1863. Since then the Universal House of Justice has acted as the head of the religion; in 1972 it published its constitution.
According to its constitution, the Universal House of Justice itself states that "The provenance, the authority, the duties, the sphere of action of the Universal House of Justice all derive from the revealed Word of Baha'u'llah which, together with the interpretations and expositions of `Abdu'l-Baha and of Shoghi Effendi ... constitute the binding terms of reference of the Universal House of Justice and are its bedrock foundation."
Originally available at the Bahá'í Study Centre (http://www.bahaistudy.org/audio-books.html).
"You may listen to the audio books on your computer, download them onto an mp3 player or record them onto a tape (45 minute per side) by plugging your cassette recorder into the headphones jack on your speakers. Unfortunately, we have not devised an order to the list. Thanks to the US's and UK's Bahá'í Service for the Blind for allowing us to use these tapes! The recordings are in the process of being re-digitized at a higher quality level. The file sizes are larger but the quality is significantly better. So, even you have heard them before, you might want to listen again."