It's common to have more than one benefit account, and it's worth knowing how they work together. Here's how your general health FSA interacts with a few common ones.
No-double-dipping rule
One rule applies across all combinations: you can't be reimbursed twice for the same expense. If more than one benefit could cover something, you (or your plan) need to choose which one pays for it.
Beyond that shared rule, here's how your FSA interacts with specific benefit types.
HSA
You can have both, but you can't contribute to an HSA while your FSA is active, since they cover the same types of expenses. If your FSA includes a grace period and you want to start contributing to an HSA right after, your FSA balance must be at $0 by the end of the prior plan year.
Dependent Care FSA
No restriction, they cover entirely different types of expenses.
HRA
Generally fine to combine, subject to the no-double-dipping rule above.
Commuter or transit benefits
No interaction at all, these fall under a completely separate part of the tax code.
Not sure about your specific combination?
Benefit interactions can get complicated, especially with plan-specific rules. If you're unsure how your benefits work together, check with a tax professional or your plan administrator.