A limited liability company (LLC) is the United States-specific form of a private limited company. It is a business structure that can combine the pass-through taxation of a partnership or sole proprietorship with the limited liability of a corporation. An LLC is not a corporation under the laws of every state; it is a legal form of a company that provides limited liability to its owners in many jurisdictions. LLCs are well known for the flexibility that they provide to business owners; depending on the situation, an LLC may elect to use corporate tax rules instead of being treated as a partnership, and, under certain circumstances, LLCs may be organized as not-for-profit. In certain U.S. states (for example, Texas), businesses that provide professional services requiring a state professional license, such as legal or medical services, may not be allowed to form an LLC but may be required to form a similar entity called a professional limited liability company (PLLC).

An LLC is a hybrid legal entity having certain characteristics of both a corporation and a partnership or sole proprietorship (depending on how many owners there are). An LLC is a type of unincorporated association, distinct from a corporation. The primary characteristic an LLC shares with a corporation is limited liability, and the primary characteristic it shares with a partnership is the availability of pass-through income taxation. As a business entity, an LLC is often more flexible than a corporation and may be well-suited for companies with a single owner.

Although LLCs and corporations both possess some analogous features, the basic terminology commonly associated with each type of legal entity, at least within the United States, is sometimes different. When an LLC is formed, it is said to be "organized", not "incorporated" or "chartered", and its founding document is likewise known as its "articles of organization", instead of its "articles of incorporation" or its "corporate charter". Internal operations of an LLC are further governed by its "operating agreement". An owner of an LLC is called a "member", rather than a "shareholder". Additionally, ownership in an LLC is represented by a "membership interest" or an "LLC interest" (sometimes measured in "membership units" or just "units" and at other times simply stated only as percentages), rather than represented by "shares of stock" or just "shares" (with ownership measured by the number of shares held by each shareholder). Similarly, when issued in physical rather than electronic form, a document evidencing ownership rights in an LLC is called a "membership certificate" rather than a "stock certificate".

In the absence of express statutory guidance, most American courts have held that LLC members are subject to the same common law alter ego piercing theories as corporate shareholders. However, it is more difficult to pierce the LLC veil because LLCs do not have many formalities to maintain. As long as the LLC and the members do not commingle funds, it is difficult to pierce the LLC veil. Membership interests in LLCs and partnership interests are also afforded a significant level of protection through the charging order mechanism. The charging order limits the creditor of a debtor-partner or a debtor-member to the debtor's share of distributions, without conferring on the creditor any voting or management rights.

Limited liability company members may, in certain circumstances, also incur a personal liability in cases where distributions to members render the LLC insolvent.

The first state to enact a law authorizing the creation of limited liability companies was Wyoming in 1977. The law was a project of the Hamilton Brothers Oil Company, which sought to organize its business in the United States with liability and tax advantages similar to those it had obtained in Panama.

From 1960 to 1997, the classification of unincorporated business associations for the purpose of U.S. federal income tax law was governed by the "Kintner regulations", which were named after the prevailing taxpayer in the 1954 legal precedent of that name. As promulgated by the Internal Revenue Service (IRS) in 1960, the Kintner regulations set forth a complex six-factor test for determining whether such business associations would be taxed as corporations or partnerships. Some of these factors had equal significance, so that the presence of only half of them would result in classification as a partnership. Accordingly, the Wyoming Legislature tailored its statute to grant LLCs particular corporate features without exceeding this threshold.

For several years, other states were slow to adopt the LLC form because it was unclear how the IRS and courts would apply the Kintner regulations to it. After the IRS finally decided in 1988 in Revenue Ruling 88-76 that Wyoming LLCs were taxable as partnerships, other states began to take the LLC seriously and enacted their own LLC statutes. By 1996, all 50 states and the District of Columbia had LLC statutes. In 1995, the IRS came to the conclusion that the widespread enactment of LLC statutes had undermined the Kintner regulations, and in 1996 it promulgated new regulations establishing a so-called "check the box" (CTB) entity classification election system that went into effect throughout the United States on January 1, 1997.