Jan Barendrecht, a regular participant on several mailing lists dedicated to the nondual perspective, defines nonduality as "the interconnectedness of everything, which is founded in the singularity of the transcendental Reality".
This may sound just too abstract and bizarre when you first hear it, but please trust me and give it a chance. If this is your first exposure to nonduality, I can almost guarantee you'll feel confused, so don't be surprised. It took me a full year to even begin to understand. Yet the rewards of understanding immeasurably outweigh the time put in. Compare it to being offered a job, difficult at first, easy later... at a payscale of ten million dollars a year. Would you take it?
Imagine losing all fear of death, unending and unbreakable inner peace under ANY circumstances, seeing beneath the surface of life right down to the deepest depths -- and beyond. This may sound like a grandiose claim, but it's within the grasp of anyone willing to dedicate a little time each day to understanding.
No strenuous effort is required, just the willingness to closely examine the nature of things, particularly what you refer to as "I" or "me." "Who (or what) am I?" is the starting point on the path. Once you begin to examine yourself seriously, the process itself takes over, and you need do nothing but cooperate. Clear seeing is effortless, and when the false is seen as false it can never fool you again.
For an encapsulated overview of the nondual perspective, please click here to view a FAQ (Frequently Asked Questions) document on the topic. This FAQ attempts to explain nonduality apart from all its religious contexts. For a full "course" on the nondual perspective, from the viewpoint of a physics professor (VERY technical in some parts), click here for "A Course In Consciousness."
In the realm of science, Quantum Physics is beginning to validate the nondual perspective (although it should be stated that it requires no scientific validation). Nonduality as a perspective stands apart from both science and religion, actually transcending both. It is all-inclusive in nature, yet does not require either faith or external proof, but only your own direct experience.
Although nonduality has often been associated with the Eastern religions, it is not incompatible with Christianity and the other Western faiths. Nonduality is a perspective that can stand apart from religion entirely, or fit together with it perfectly. It is neither affirmed nor denied in traditional Judaism, Islam or Christianity, although all these religions have a "mystical" branch that incorporates the nondual perspective (Quabalah, Sufism and Gnostic Christianity, respectively). All of these "mystical" branches of religion emphasize direct experience of, and even merging with the divine, rather than emphasizing the division between "creator" and "creation." According to nondualism in a spiritual or religious context, creator and creation are not-two. In other words, God cannot be separated from creation -- they are one and the same thing.
Many of the pages linked to on the left-side menu explain the basic precepts of nonduality (and the basics are common to all the nondual religions and viewpoints). I hope you enjoy exploring the many local and remote links on The Core.