# IGrainObserver

Package: [Microsoft.Orleans.Core.Abstractions](/orleans/docs/api/csharp/microsoft.orleans.core.abstractions/) 10.0.0

[NuGet package](https://www.nuget.org/packages/Microsoft.Orleans.Core.Abstractions)

```csharp
public interface IGrainObserver : IAddressable
```

A marker interface for grain observers. Observers are used to receive notifications from grains; that is, they represent the subscriber side of a publisher/subscriber interface.