Foundations of World Unity is a collection of talks and writings of `Abdu'l-Bahá, dated prior to his death in November 1921, and first published in 1945. The introduction to the 1945 edition is dated 1927.
It includes mainly selected talks from Promulgation of Universal Peace, and a few passages from Bahá'í Scriptures, Selections from the Writings of 'Abdu'l-Bahá and Some Answered Questions.
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."