The importance of selecting the right pot to plant your Bonsai in is often underestimated. The pot (as well additions like grasses, moss, stones, figurines and a bonsai table) are important elements of the composition, and should be chosen carefully to display the tree.
Bonsai are planted in small pots, often imported from Japan or China. Japanese pottery is known for its high quality and are often quite expensive, elegant, natural and unglazed, whereas Chinese pottery is generally cheaper (quality is getting better and better though) and often brightly glazed. An exception however is antique Chinese pots, which are priceless and very rare.
Old Bonsai trees, which do not need to be trained anymore and have been repotted and root-pruned many times already, are adapted to living in small pots. Younger trees however, need more room to grow and will be trained step-by-step to adept to living in increasingly smaller bonsai pots, by pruning their roots every time they are being repotted. Young trees can be planted in less expensive pots or plastic containers, widely available at (online) Bonsai shops.
Trees still being trained should be placed in rather large containers, providing the roots with enough space to grow and help the tree to cope with intense training techniques applied, like style-pruning. Older trees have a more compact root-system and can be planted in smaller Bonsai pots, aesthetic considerations are more important in this case.
Above: A glazed and an unglazed Bonsai pot.
Choosing a pot that really suits the tree is difficult, as different variables (like shape, choosing between glazed/unglazed and color) need to be taken into account. A few basic guidelines can be used to select the right pot (these should not be taken as strict rules; aesthetic considerations tend to be highly personal!):
Finally, it is most important to select a container that is large enough for the tree to sustain its health and to use a pot that is, in terms of design, subordinate to the tree (simplicity is often key). For inspiration, take a look at trees and their pots in the Bonsai gallery.