A tax election, not a kind of company - what electing S status does to how a corporation or LLC is taxed, who is eligible to make it, and how it is lost.
An S corporation is not a separate type of business entity. It is an ordinary corporation, or an LLC that has chosen to be taxed as a corporation, that has elected under Subchapter S of the Internal Revenue Code to have its income, losses, deductions and credits passed through to its owners and reported on their personal returns, instead of being taxed at the company level and again when distributed. The entity itself is still formed, governed and sued under state law exactly as before; only its federal tax treatment changes, and the state's treatment follows only where the state has chosen to conform.
Eligibility is what makes the election fragile. The code limits how many shareholders an S corporation may have and who they may be - individuals, certain trusts and estates, and not partnerships, most corporations or non-resident aliens - and permits only one class of stock, so that every share carries identical rights to distributions and liquidation proceeds. The election is made on a form signed by every shareholder and, to take effect for a given year, must be filed within a window early in that year. Admitting an ineligible shareholder, issuing a second class of stock, or an LLC operating agreement that allocates distributions unequally can terminate the election involuntarily, sometimes without anyone noticing until an audit.
The election is usually made to reduce self-employment tax: an owner who works in the business is paid a salary, subject to payroll taxes, and takes the remaining profit as a distribution that is not. The Internal Revenue Service requires that salary to be reasonable compensation for the work actually done, and recharacterises distributions as wages when it is not. Whether the election saves anything depends on the owner's facts, the state's treatment of S corporations, and the cost of running payroll.
A business owner considering the election should have both a tax adviser and a lawyer look at it, because the tax saving is an accounting question and the eligibility rules are a drafting question: the operating agreement or shareholders' agreement has to keep every owner and every share inside the code's limits for as long as the election is meant to last. An owner who has just learned the election may have terminated should get advice before filing anything, since relief for an inadvertent termination exists but has to be requested properly.
Choose your state. Each link opens the directory page for the city in that state with the most currently published law firms in this practice area; a +n beside the city is how many other cities in the state also have one. The list is generated when this page loads, so a state whose listings have lapsed drops out rather than becoming a dead link.