We like this definition for its simplicity. Hits the nail on the head:

"Permaculture is the science and art of integrating and connecting indigenous resources with available appropriate technology to mimic natural processes. Doing so, we take care of the Earth and promote sustainable living." - Camilo O'Kuinghttons

Another favorite definition is Larry Santoyo's. Larry is one of the preeminent permaculture designers in the world. Check out his site, Earthflow.

"Permaculture is the art and science that applies patterns found in nature to the design and construction of human and natural environments. Only by applying such patterns and principles to the built environment can we truly achieve a sustainable living system. Permaculture principles are now being adapted to all systems and disciplines that human settlement requires. Architects, planners, farmers, economists, social scientists, as well as students, homeowners and backyard gardeners can utilize principles of Permaculture Design." - Larry Santoyo

David Holmgren was the research student and co-originator with Bill Mollison, his research supervisor, of the permaculture concept:

"Permaculture is a design system based on ethics and principles which can be used to establish, design, manage and improve all efforts made by individuals, households and communities towards a sustainable future." - David Holmgren

Larry Korn worked extensively with Masanobu Fukuoka:

"Bill Mollison has devised a concept of consciously designed, self-sustaining ecosystems which he refers to as "permaculture." His system, involving a great diversity of plant and animal species, emphasizes the importance of tree crops and other perennial plants wich have multiple beneficial uses in the landscape. The elements are designed into an integrated system which takes advantage of the unique conditions and attributes of each site. They are arranged in such a way that the species which require the greatest attention and care are located closest to the dwelling site, while the plants and animals that require less attention are placed on the periphery. By careful design, energies which enter the area from the outside, such as wind, sunlight, water, fire and wildlife, are encouraged or screened so they work to the benefit of the whole system. The idea is to design a perennial, highly productive ecosystem which, once established, will operate with a minimum of maintenance."
- Larry Korn from the intro to The Future is Abundant.

And here, Bill Mollison's answer to being asked to define permaculture by Alan AtKisson in 1991 for a radio interview. Truly priceless:

"Alan: Permaculture is a slippery idea to me. But from what I read, it seems that not even those who actually do permaculture really know what it is.

Bill: I'm certain I don't know what permaculture is. That's what I like about it - it's not dogmatic. But you've got to say it's about the only organized system of design that ever was. And that makes it extremely eerie.

Alan: Why "eerie"?

Bill: There's no other book about design for living. Don't you think that's eerie? I mean, how can we possibly expect to survive if we don't design what we're doing to be bearable? Another thing I find extremely eerie is that when people build a house, they almost exactly get it wrong. They don't just get it partly wrong, they get it dead wrong. For example, if you let people loose in a landscape and tell them to choose a house site, half of them will go sit on the ridges where they'll die in the next fire, or where you can't get water to them. Or they'll sit in all the dam sites. Or they'll sit in all the places that will perish in the next big wind.

But then, at least half of every city is wrong. From latitude 30 degrees to latitude 60, say, you've got to have the long axis of the house facing the sun. If the land is cut up into squares, that makes half of all houses wrong if they face the road. Even houses way in the country, and way off the road, face the bloody road. And from there, you just go wronger all the way.

One of the great rules of design is do something basic right. Then everything gets much more right of itself. But if you do something basic wrong - if you make what I call a Type 1 Error - you can get nothing else right.

Alan: When you say "we," do you mean humans in general, or Western humans especially?

Bill: Human beings in general. There are a few societies that show signs of having been very rational about the physics of construction and the physics of real life. Some of the old middle-Eastern societies had downdraft systems over whole cities, and passive, rapid-evaporation ice-making systems. They were rational people using good physical principles to make themselves comfortable without additional sources of energy.

But most modern homes are simply uninhabitable without electricity - you couldn't flush the toilet without it. It's a huge dependency situation. A house should look after itself - as the weather heats up the house cools down, as the weather cools down the house heats up. It's simple stuff, you know? We've known how to do it for a long time.

Alan: And it's eerie that we don't do it.

Bill: And that we don't design the garden to assist the house is much more eerie. That we don't design agriculture to be sustainable is totally eerie. We design it to be a disaster, and of course, we get a disaster.

Alan: There's an old Chinese expression: "If we don't change our direction, we'll wind up where we are headed."

Bill: Exactly so. I think we probably have a racial death wish. We don't understand anything about where we live, and we don't want to. We're happy to power on to the end - like Mr. Bush. He could have saved more oil than he needed from Iraq, but he preferred to go and "kick ass" - kill people - and use more oil in the process.

America is an eerie society. It seems to want to live on a dust bowl. But as one of your own Indians said, "If you shit in bed, you'll surely smother in it."

Alan: Let's get back to permaculture. What's your current best definition of it?

Bill: You could say it's a rational man's approach to not shitting in his bed.

But if you're an optimist, you could say it's an attempt to actually create a Garden of Eden. Or, if you're a scientist, you could liken it to a miraculous wardrobe in which you can hang garments of any science or any art and find they're always harmonious with, and in relation to, that which is already hanging there. It's a framework that never ceases to move, but that will accept information from anywhere.

It's hard to get your mind around it - I can't. I guess I would know more about permaculture than most people, and I can't define it. It's multi-dimensional - chaos theory was inevitably involved in it from the beginning.

You see, if you're dealing with an assembly of biological systems, you can bring the things together, but you can't connect them. We don't have any power of creation - we have only the power of assembly. So you just stand there and watch things connect to each other, in some amazement actually. You start by doing something right, and you watch it get more right than you thought possible."

Enough said.