Rust's signature achievement is memory safety without a garbage collector. It accomplishes this through a disciplined ownership system — but that system deliberately has an escape hatch: reference counting.
Every value in a Rust program has a single owner at any given time. When that owner goes out of scope, the value is dropped — memory freed, deterministically, at a known point in execution. No GC pause, no dangling pointer, no double-free. The compiler enforces all of this statically.
But some data genuinely needs to be shared: a node in a graph owned by multiple edges, a configuration object threaded through many subsystems, a callback holding a reference into surrounding state. Enter reference counting — Rc<T> and Arc<T> — which shift ownership logic from compile time into a small runtime counter.
These are not competing features. They are complementary tools with distinct trade-offs. This article unpacks both — semantics, performance, ergonomics, and the decisive question: which should you reach for?