LLCs are typically taxed on a pass through basis, much like general partnerships. As pass through entities, the profits and losses of LLCs are passed on to the individual owners and are reflected on the owner’s personal income tax returns. Alternatively, LLCS may elect to be taxed as S corporations to potentially reduce the self-employment taxes imposed on the owners.
A series LLC is a form of limited liability company that provides liability protection to multiple "series". Essentially, it's a master LLC with separate divisions, each protected and operating independently. As an entity, the series LLC is geared towards businesses where investors own multiple companies, with each series being protected from the debts and obligations of the other series. Currently, only several states support this option, including Delaware, Illinois, Iowa, Nevada, Oklahoma, Puerto Rico, Tennessee, Texas, and Utah.
Depending on elections made by the LLC and the number of members, the IRS will treat an LLC as either a corporation, partnership, or as part of the LLC’s owner’s tax return (a “disregarded entity”). Specifically, a domestic LLC with at least two members is classified as a partnership for federal income tax purposes unless it files Form 8832 and affirmatively elects to be treated as a corporation. For income tax purposes, an LLC with only one member is treated as an entity disregarded as separate from its owner, unless it files Form 8832 and elects to be treated as a corporation. However, for purposes of employment tax and certain excise taxes, an LLC with only one member is still considered a separate entity.
Filing a limited liability company separates your personal assets from those of your business. This prevents you from being financially responsible for debts and liabilities of your business. Even though members are still liable, that liability is limited to the extent of their investments in the business. If, for instance, your company is involved in a lawsuit, the assets of the LLC itself could be in jeopardy, while the personal assets of the members/owners would be protected.