I posted a brief summary about permaculture recently.
Designs stress ecological connections and closed energy and material loops.
The core of permaculture is design and the working relationships and connections between all things. Each component in a system performs multiple functions, and each function is supported by many elements. Permaculture designs have been successfully and widely implemented in third-world countries, but there is current need to expand these principles in temperate climates, and especially urban areas to create more enjoyable and sustainable human habitats. This is what may be interesting to those who want to see an application of principles already known, rather than another body of theoretical knowledge. So a book written in sub-tropical Australia may not be directly appropriate to Temperate North America or the UK, since species and planting information is likely to be different.