The Teachings of Ajahn Chah
Ajahn Chah was possibly the most influential monk regarding the dissemination of Theravada Buddhism in the West. There are multiple monasteries in the USA and the UK that he had instituted during his ministry. Amaravati Monastery and Abhayagiri Monastery are just two of the many that have sprung up in the last 50 years or so.
His official website is https://ajahnchah.org/, however the Venerable Ajahn Chah passed on in 1992 and due to his residence primarily in Thailand, the recorded teachings of him are somewhat sparse. The PDF, made available above, weighs in at a hefty 725 pages, but that is pretty much everything that was recorded during his life.
He spent much of his time at Wat Nong Pah Pong Monastery which he founded in 1954, where he, to quote his website:
led a simple and pure life in a harmoniously regulated community where virtue, meditation and understanding may be skillfully and continuously cultivated.
Wat Nong Pah Pong currently has over 200 branch monasteries in Thailand alone. Ajahn Chah was one of the first Thai monks to ordain westerners into the Thai Forest tradition and thus started the spread of his valuable teachings to the West.
The Teachings of Ajahn Chah are made available on this site under the agreement cited within the PDF document. That is to say, it can be freely distributed, electronically. To distribute hard copies then permission must be obtained from the original publisher.