# Handlers and Sagas


There are two standard ways of executing code when a message is processed: [handlers](handlers/index.md) and [sagas](sagas/index.md).

Handler instances are instantiated on a per-message basis, executed, and then disposed of. These are sometimes referred to as "stateless handlers".

Saga instances are also instantiated on a per-message basis, executed, and then disposed of. However they differ from handlers in that, once instantiated, they are passed an instance of a "Data" class. The "Saga Data" is the persisted state for an instance of a given saga type that is identified by a key. These are sometimes referred to as "stateful handlers".

Other concepts that both handlers and sagas share:

 * [Recoverability](/nservicebus/recoverability/index.md) (i.e. what happens when message processing fails)
 * Executed within the same [pipeline](/nservicebus/pipeline/index.md)
 * Registered via [handler and saga registration](handlers-and-sagas-registration.md)