+++
title = "Write an expression"
weight = 20
aliases = ["/docs/sources/panels/query-a-data-source/use-expressions-to-manipulate-data/write-an-expression/"]
+++

# Write an expression

If your data source supports them, then Grafana displays the **Expression** button and shows any existing expressions in the query editor list.

For more information about expressions, refer to [About expressions]({{< relref "./about-expressions.md" >}}).

## Before you begin

- [Add a panel]({{< relref "../../working-with-panels/add-panel.md" >}}).

**To write an expression**:

1. Open the panel.
1. Below the query, click **Expression**.
1. In the **Operation** field, select the type of expression you want to write.

   For more information about expression operations, refer to [About expressions]({{< relref "./about-expressions.md" >}}).

1. Write the expression.
1. Click **Apply**.