# AddSystem<T>(T)

> Obsolete. Use World.AddSystemManaged instead.

## Definition

* **Type:** Method
* **Namespace:** [Unity.Entities](/engine/7000.0/script-reference/unity/entities.md)
* **Assembly:** UnityEngine.EntitiesModule

> **Warning:**
>
> **Removed.** This API has been removed and is no longer supported.
>
> **Upgrade to** [World.AddSystemManaged](/engine/7000.0/script-reference/unity/entities/world/addsystemmanaged.md)

```csharp
public T AddSystem<T>(T system) where T : ComponentSystemBase
```

### Parameters

**** (T): The existing system instance to add

### Returns

| Type | Description        |
| ---- | ------------------ |
| T    | The input `system` |