| Exceptions | Utility class to help propagate checked exceptions and rethrow exceptions designated as fatal. |
| CompositeException | Represents an exception that is a composite of one or more other exceptions. |
| MissingBackpressureException | Indicates that an operator attempted to emit a value but the downstream wasn't ready for it. |
| OnErrorNotImplementedException | Represents an exception used to signal to the RxJavaPlugins.onError() that a
callback-based subscribe() method on a base reactive type didn't specify
an onError handler. |
| ProtocolViolationException | Explicitly named exception to indicate a Reactive-Streams protocol violation. |
| UndeliverableException | Wrapper for Throwable errors that are sent to `RxJavaPlugins.onError`. |