3D printing or additive manufacturing is the process of printing three dimensional objects from designs made on a computer. It has been around since the 1980s but only used for prototyping in large scale companies. Now a revolution is under way. With 3D printers available for less than £2000 they are quickly appearing in the domestic market. MakerBot being a notable example.
You can print more or less any shape / object using a variety of materials, metal, plastic, paper and even food substances! The uses for 3D printing are seemingly endless! As someone who enjoys tinkering with my car on a daily basis the ability to print out spare parts would save endless trips to the main dealer or frequent eBay searches. Already thousands of free designs are available on the Internet, take a look at Thingiverse for some of the great offerings.
So how can 3D printing change the world? As I see it the world economy is driven by the classic model of supply and demand. Objects like diamonds are scarce (i.e. there is low supply) therefore the price is high. Although 3D printers can't make diamonds yet they can make a lot of other things (even guns) and no longer will you need to pop to the shops for a lot of things. Imagine the handle of your favourite coffee mug snaps off, no problem! Just print another one off. And why stop at a single mug, why not print 12 off?
3D printing will increase supply of goods (i.e. making them less scarce) and therefore price will have to fall. I believe supply could be so great that prices will fall to zero! I haven't even got to the best bit yet about all this. Currently a 3D printer can print approximately 70% of its own components, in the coming years this will inevitably become 100%. Some progress has already been made by The University of Bath: http://en.wikipedia.org/wiki/RepRap_Project - This means you won't need to go to PC World or wherever to buy another one if it breaks. You simply ask a friend or neighbour to print a 3D printer for you on their 3D printer! You could have one in every room of your house.
The potential applications for 3D printing are huge, I see it being particularly useful in many impoverished places of the world. The ability to print out spare parts for generators, water pumps and even medical applications. If 3D printing is able to give us all the things we want at the touch of a button will there be any need for money? Will humanity move from a monetary based economy to a resource based one?