> ## Documentation Index
> Fetch the complete documentation index at: https://zenml.mintlify.site/llms.txt
> Use this file to discover all available pages before exploring further.

# Controlling the Step Execution Order

> How to control the order in which steps get executed

By default, ZenML uses the data flowing between steps of your pipeline to determine the order in which steps get executed. The following example shows a pipeline in which `step_3` depends on the outputs of `step_1` and `step_2`. This means that ZenML can execute both `step_1` and `step_2` in parallel but needs to wait until both are finished before `step_3` can be started.

```py
from zenml.pipelines import pipeline

@pipeline
def example_pipeline(step_1, step_2, step_3):
    step_1_output = step_1()
    step_2_output = step_2()
    step_3(step_1_output, step_2_output)
```

If you have additional constraints on the order in which steps get executed, you can specify non-data dependencies by calling `step.after(some_other_step)`:

```py
from zenml.pipelines import pipeline

@pipeline
def example_pipeline(step_1, step_2, step_3):
    step_1.after(step_2)
    step_1_output = step_1()
    step_2_output = step_2()
    step_3(step_1_output, step_2_output)
```

This pipeline is similar to the one explained above, but this time ZenML will make sure to only start `step_1` after `step_2` has finished.