The Jhanas are eight altered states of consciousness which can arise during periods of strong concentration. The Jhanas are naturally occurring states of mind, but learning how to enter them at will and how to stay in them takes practice.
Their principle use in Buddhist meditation is to generate ever increasing
levels of concentration so that later when the meditative mind is turned to
a practice that tends towards wisdom, it can do that practice with far less
Below are links to several places on the 'net where the Jhanas are discussed.
Some of these pages are mine; some are at other sites I've found.
Sharpening Manjushri's Sword
The Jhanas in Theravadan Buddhist Meditation ~ Leigh Brasington
This is revised edition of a paper I presented to the American Academy of Religion/Western Regional meeting on 25 Mar '97. It contains a bibliography and links to other sites that discuss the Jhanas.
Instruction for Entering Jhāna ~ Leigh Brasington
This is a reprint of an article that first appeared in Insight Journal, Fall 2002.
It is a transcription of a talk I gave at the Barre Center for Buddhist Studies in April of 2002.
Interpretations of the Jhanas. ~ Leigh Brasington
There is no real agreement among Jhana teachers as to what exactly the Jhanic state are! This paper outlines the various methods that I have heard about.
How Many Jhānas Are There? ~ Leigh Brasington
My personal research has turned up no less than 25 different states that are identified by the word Jhāna in ancient Pali literature - and even more uses of jhāna in modern times.
in Theravadan Buddhist Meditation ~ Maháthera Henepola Gunaratana
This classic book on the jhanas is now available on the 'net.
Ajahn Brahmavamso is a Theravaden Buddhist monk who lives in Western Australia.
He studied extensively with Ajahn Cha in Thailand as well as in other places before
returning to Australia. His definition of exactly what constituted a Jhana
seems to imply Much stronger absorption than my own definition - or that of other
Westerners I have discussed the Jhanas with (such as Ayya Khema,
Thanissaro Bhikkhu and others).
He has given several talks on the Jhanas which have been transcribed and now appear on the 'net:
"Nimitta, nimitta, who's got a nimitta?" Ever wonder why the suttas don't mention "nimitta" but that "nimitta" is so important in the Visuddhimagga? Definitely read The Mystery of the Breath Nimitta ~ Bhikkhu Sona.
The first Western conference on Jhana practice in Theravada Buddhism
was held near Santa Fe, New Mexico, USA, in June, 2001. See Lloyd Burton's report
Gathering Fruit and Planting Seeds for the details.