A series LLC is a single legal entity that can create multiple internal "series," each with its own assets, liabilities, and members — designed to wall off liability between different business lines or properties without forming a separate LLC for each one.
Where it's actually used
Series LLCs are popular with real estate investors holding multiple properties, since each property can sit in its own series — a liability arising from one property theoretically shouldn't expose the assets in another series within the same parent LLC.
Not every state recognizes them
Series LLC statutes only exist in a subset of states, and states that don't have enabling legislation may not respect the liability separation between series, even if the LLC was formed in a state that does allow it — a critical detail for anyone operating across state lines.
Maintaining the separation is essential
The liability protection between series depends on keeping their finances, records, and operations genuinely separate — commingling funds or failing to maintain distinct records for each series can undermine the very protection the structure is meant to provide.
Weighing it against simply forming multiple LLCs
A series LLC can reduce filing fees and administrative overhead compared to forming a separate LLC for each property or business line, but the legal uncertainty in states without clear series LLC law is a real tradeoff worth weighing before choosing this structure over more established alternatives.