Is there any kind of business model where all the owners are also workers?

Wouldn’t this eliminate the need for unions? There would be no “evil boss” because the bosses would all be elected by the people they work under. The true people who actually put in the mental and physical effort to make the business a success share in all the profits.

Is there any legal structure for a business to exist in this form?

Yes, it’s called a “corporation.” Any corporation could be worker-owned, if the workers in question had the bucks to make it happen.

There is also a business model in which workers must be owners – it’s called a coöperative.

It’s referred to as an “employee-owned corporation”.

There are any number of them. I believe Toys R Us is one of them. Or at least, one of the major toy store chains.

I’ve heard that they tend to be very efficient.

“Employee owned” companies certainly exist, though the arrangement is not as egalitarian as you are undoubtedly thinking (in most cases the “employee ownership” includes managers who have very large blocks of stock, and there may be some founders about who also have very large slices of the pie. A few large stockholders still typically have enough shares to control the corporate destiny):

http://www.saic.com/empown/
http://www.nceo.org/library/eo100.html

There is nothing to stop you from having a company function completely as a “cooperative” in which the rank and file employees held elections to choose management, determine policy, etc.

I suspect the problems would arise in the solution not scaling, and being inefficient. At some point, you need capital for new operations, and guess what the outsider willing to give you the money wants in return (or you do an IPO, and, guess what, you now have public shareholders). And while you are in the process of democratically deciding the corporate course of action or leadership, your autocratic competetion eats your lunch in the marketplace.

What you describe is pretty much the way a partnership works, too. Of course, the partnership model wouldn’t work very well in something as large as a modern corporation, if that’s what you’re talking about…

Yes, it’s called a “corporation.” Any corporation could be worker-owned, if the workers in question had the bucks to make it happen.

There is also a business model in which workers must be owners – it’s called a coöperative.

A blurb on cooperatives:

http://www.ncba.coop/primer.cfm

I should have been clearer that many small businesses operate as cooperatives, and the problems I alluded to attach to trying to use a cooperative model for a large operation.

Partnerships actually work quite well for firms that have thousands of employees as long as they are professional service firms (law firms, accountants, technical consultants) where most employees have at least the potential to someday join the partnership.

Toys R Us is a publically traded company (NYSE:TOY). It could still be called “employee owned” if a controlling interest was maintained by the employees, but that doesn’t seem to be the case:

http://finance.yahoo.com/q/ks?s=TOY

They have about 213M shares outstanding, 211M of which are float. What does look slightly unusual is that 95% of the ownership is institutional. That’s rather high. Here’s the big holders:

http://finance.yahoo.com/q/mh?s=TOY

The vast majority of corporations in this country are not the large ones with shares publicly traded on major stock exchanges, but rather small, privately-held companies. For those enterprises, particularly when they are just starting out, it would not be unsual at all for the owners to also be the only employees of the company.

Hell, almost every dot-com company hired people on the promise “we won’t pay you much, but we’ll give you lots of stock.” Almost all of those employees were also owners, although their ownership ended up being worthless.