# Activity Execution - .NET SDK

> For the complete documentation index, see [llms.txt](https://docs.temporal.io/llms.txt).
> Any documentation page is available as raw Markdown by appending `.md` to its URL.

> Call an Activity from a .NET Workflow with ExecuteActivityAsync, set the required Schedule-To-Close or Start-To-Close Timeout, and await the result.

## Start an Activity Execution 

Calls to spawn [Activity Executions](/activity-execution) are written within a [Workflow Definition](/workflow-definition).
The call to spawn an Activity Execution generates the [ScheduleActivityTask](/references/commands#scheduleactivitytask) Command.
This results in the set of three [Activity Task](/tasks#activity-task) related Events ([ActivityTaskScheduled](/references/events#activitytaskscheduled), [ActivityTaskStarted](/references/events#activitytaskstarted), and ActivityTask[Closed]) in your Workflow Execution Event History.

A single instance of the Activities implementation is shared across multiple simultaneous Activity invocations.
Activity implementation code should be _idempotent_.

The values passed to Activities through invocation parameters or returned through a result value are recorded in the Execution history.
The entire Execution history is transferred from the Temporal Service to Workflow Workers when a Workflow state needs to recover.
A large Execution history can thus adversely impact the performance of your Workflow.

Therefore, be mindful of the amount of data you transfer through Activity invocation parameters or Return Values.
Otherwise, no additional limitations exist on Activity implementations.

To spawn an Activity Execution, use the `ExecuteActivityAsync` operation from within your Workflow Definition.

```csharp
using Temporalio.Workflows;

[Workflow]
public class MyWorkflow
{
    public async Task<string> RunAsync(string name)
    {
        var param = MyActivityParams("Hello", name);
        return await Workflow.ExecuteActivityAsync(
            (MyActivities a) => a.MyActivity(param),
            new() { StartToCloseTimeout = TimeSpan.FromMinutes(5) });
    }
}
```

Activity Execution semantics rely on several parameters.
The only required value that needs to be set is either a [Schedule-To-Close Timeout](/encyclopedia/detecting-activity-failures#schedule-to-close-timeout) or a [Start-To-Close Timeout](/encyclopedia/detecting-activity-failures#start-to-close-timeout).
These values are set in the Activity Options.

### Get the results of an Activity Execution 

The Activity result is returned in the Task from the `ExecuteActivityAsync` call.