Serde is Rust's serialization framework, supporting JSON, YAML, TOML, MessagePack, and more through format-specific crates. With #[derive(Serialize, Deserialize)], your structs automatically convert to and from these formats. Serde is extremely fast because it generates specialized code at compile time and can borrow from the input (&str fields) without copying. I use serde_json for APIs, serde_yaml for config files, and bincode for binary protocols. The #[serde(rename = "...")] attribute maps Rust field names to external formats. For custom serialization, you can implement the traits manually. The ecosystem is mature, well-documented, and integrates with async I/O seamlessly. It's essential for any networked Rust application.