Spring onions are sometimes known as eschallots: they're the tall thin bunching onions, for salads,stir-fries etc.
Shallots look more like a small brown onion,complete with papery skin.They're more bitter and are used for making curry pastes, etc, and more traditional French recipes.
However, it seems that on a lot of websites, the names are interchangeable.

g'day blackcat,

as andy says often spring onions are misnamed shallots/eschallots(correct spelling), we grow a perennial bunching onoin and others call it a spring onion? it may look the same but it doesn't have the same growth pattern.

len

Here is a link that might be useful: lens garden page

New South Welshmen are notorious for mixing up the two. Victorians seem to know better. It's a bit complicated, but lets start.
There are two species of onion, Allium cepa, the usual European onion, and Allium fistulosum, the onion of China and Japan.
both species have many varieties.
The European onion usually has large bulbs - eg salad and cooking onions. But it also has small tasty bulbs - yellowish or reddish, that are named shallots because they originally were transported from Eschalon on the eastern shore of the Mediterranean. These are the small bulbs favoured in French cooking, but also fried in south-east Asian dishes, and often to be found at Asian grocers
Europeans also traditionally picked young European onions in the spring for salads or plain eating, with a hot spicy flavour. These were known as 'spring onions'.

Allium fistulosum is the traditional onion of China and Japan. It is much milder in flavour and does not bulb up very much at all. It is picked with the green stem and leaves. It too has many varieties. Europeans in the past tended to call this a Welsh onion or a 'bunching onion' because it often multiplies in the ground into little bunches.
But then people called it spring onion because the bunches looked like bunches of traditional western spring onions. Why some people started to call them shallots, I do not know, but I do know, very confusingly, that some Vietnamese market gardeners here plant western shallots, and sell the emerging greens as a substitute for Asian onions. Confused?
I prefer to call them western onions and oriental onions, or to use the Japanese name 'negi' for Allium fistulosum. And then it is only a small step to delve into the wonders of oriental onions such as ishikura, long and white, readily available here, shimonita, which is as fat as a leek, or the wonderful 'naga negi' (snake negi) which can grow to be two feet long, or the one I grow, kabuki negi (heading negi) with it's reddish tinted shanks.
The two species can be told apart easily by looking at the point at which leaves insert into the stem. The leaf insert is round in a western onion, and half-moon shaped in an oriental onion.