How many people do you know who have an apple tree in their garden? Maybe quite a few... What is uncommon is to have a large variety of different fruit trees in your garden. How many people do you know who grow apples, pears, lemons in their backyards?
The reason is quite simple. The trees are way too big to have more than just 1 or 2...right?
Wrong!
Fortunately, there is a way to grow fruit trees in such a way that you can have your own orchard if you want to.
Welcome to the World Of Rootstocks.
If your not aware, go and have a look at fruit trees in your local garden centre and look at the base of them. You will see a tree in a container and a knobbly bit a few inches up the tree stem. The bit of the tree in the soil is the rootstock, and the rest of the tree is the variety of fruit attached to it.....(the scion to those in the know 
). The knobbly bit that joins the two together is where the rootstock and scion have been 'grafted' together.
I dont know how to embed videos on my site but if you click on the link it will take you a video I made showing you what a graft looks like..The Knobbly Bit
The typical apple tree you buy from the garden centre is probably grafted on a M26 or MM106 rootstock, and produces a nice-looking tree about 12ft-15ft in height and a similar spread.
But for our purposes this isn't what we want, MM106 is far too big for us. What we want is a tree that will be about 6ft high or less.
Now don't be put off by these weird looking letters and numbers. All you need to know is the variety of tree you want and what size you want it to be at maturity. Your garden centre or supplier will do the rest for you. But if you want to be a bit more knowlegable...and why wouldn't you?.. Then you need to get an idea of what rootstocks are.
Because this site is specific to Dwarf Fruit Trees then that is where we will concentrate.
First thing to take note is this....There is no such thing as 1 rootstock type that you can use for all your trees. Different rootstocks are required for different fruits. Here in the UK (where I live) I use the following rootstock types:
M27 Rootstock
Apples
Extremely dwarfing rootstock for apples. Trees dwarfed to 6-8 ft, ideal for high density planting, small spaces in garden, tub growing. Induces early and heavy bearing. Small root system, young trees may need staking. Good for container growing.
Quince C Rootstock
Pears
Quinces
Medlars
At maturity the tree will be 9ft to 16ft...but you can prune to keep the height down.
Gisela 5 Rootstock
Cherries
This rootstock will give you a tree that will be about 10ft in height.
Pixy Rootstock
Plums
Peaches
Necerines
Apricots
This rootstock will give you a tree that will be about 10ft in height.
There are many rootstocks available these days but these are the ones I am most familiar with. So if you go to your supplier and say " I want to grow a Plum tree that I can keep at about 10ft high on a Pixy type rootstock" then you wont go far wrong.
I heartily recommend The Backyard Orchardist if you want to know more. Heres a blurb of text about the book:
"For every gardener desiring to add apples, pears, cherries, and other tree fruit to their landscape here are hints and solid information from a professional horticulturist and experienced fruit grower. The Backyard Orchardist includes help on selecting the best fruit trees and information about each stage of growth and development, along with tips on harvest and storage of the fruit. Those with limited space will learn about growing dwarf fruit trees in containers.
Appendices include a fruit-growers monthly calendar, a trouble-shooting guide for reviving ailing trees, and a resource list of nurseries selling fruit trees."