From the Transition Network:

Transition is a quiet revolution unfolding around the world. People are seeing crisis as the opportunity for doing something different, something extraordinary. 
It's an idea about the future, an optimistic, practical idea. And it's a movement you can join. There are people near you who are optimistic and practical too. And it's something you can actually do.
Transition is one manifestation of the idea that local action can change the world; one attempt to create a supportive, nurturing, healthy context in which the practical solutions the world needs can flourish. You may have heard of it as 'Transition towns', or you may have come across a Transition group where you live. It is an experiment kicked off by people who share this passion, one that has gone far and wide, popping up in the most unexpected of places, in thousands of communities in 40 countries around the world.
The aim of Transition is to help you be the catalyst in your community for an historic push to make where you live more [[resilience|resilient]], healthier and bursting with strong local livelihoods, while also reducing its ecological footprint. 
You could think of Transition as being the bit in the middle, between things you can do as an individual and all the big stuff government can do.  It’s something that can only happen from the ground up, driven by ordinary people.  It’s the missing piece of the puzzle.
(read more at the Transition Network)