There are two basic types of Limited Liability Companies (LLCs): member managed and manger managed. There are three less common types: Series LLCs, Single Member LLCs, and Professional LLCs.
Member Managed LLC
The members, or owners, a limited liability company manage, or operate, the business in a member managed LLC. The LLC Operating Agreement spells out the rights and responsibilities member managers.
Manager Managed LLC
The members of an LLC may hire a manager to operate the business in a manager managed LLC. The manager may be a natural person like a Chief Executive Officer. The members may appoint an other business (legal entity) as the manager.
There are three additional types of LLC depending on jurisdiction: single member LLC, series LLC, and professional LLC.
A Series LLC is a single limited liability company that controls "series" of LLCs within its structure. Each series is like a standalone legal entity. The debts and obligations of one series do not, generally, spill over to the other series or to the main LLC.
Single member LLC
A single member LLC is an LLC with one member. LLCs provide a corporate veil protecting the assets of member. A single member LLC carries more risk of piercing the corporate veil, because it can be difficult to differentiate the actions of the individual owner and the business.
Some states authorize professional LLCs (or PLLC). Individuals with certain licenses must own a certain percentage of the company, often more than 50%.