A Series LLC lets you run what looks like multiple LLCs under a single parent umbrella, with each series legally protected from the debts and lawsuits of the others. It was designed to reduce the formation, registration, and annual fee burden of managing many separate LLCs across a large rental portfolio. Instead of forming 10 LLCs in Texas and paying 10 annual fees plus 10 sets of registered agent fees, you form one Series LLC and create 10 series under it, each holding one or more properties with its own assets and liabilities walled off from the others. Series LLCs are currently recognized in around 18 states including Texas, Delaware, Illinois, Tennessee, and Nevada. The downsides are meaningful. Not all states recognize the series liability shield, so a lawsuit in a non recognizing state may pierce all your series at once. Some lenders and insurers refuse to work with Series LLCs because the structure is still legally untested in many jurisdictions. For a large portfolio in a recognizing state, a Series LLC can dramatically simplify operations. For smaller portfolios or multi state portfolios, standard LLCs are usually the safer choice.
Example
You form a Series LLC in Texas and create 8 series under it. Each series holds one Birmingham rental. A tenant at Series 3 sues and wins a judgment. The liability shield protects Series 1, 2, 4, 5, 6, 7, and 8 and their assets from the judgment.