# Overview

Learn how to use event expressions in CQL.

Event expressions let you define conditions based on the history of events in a user's journey. For example, you can check whether a user viewed a specific page today or yesterday, or if they recently abandoned a cart.

## Syntax

An event expression starts with an event type, and may include criteria, a quantifier, or a time window:

```cql
user has /*<event>*/ /*<criteria>*/ /*<quantifier>*/ /*<window>*/
```

You can also use negation with `not`:

```cql
user has not /*<event>*/
```

Here's how you could check if a user has shown interest in smartphones:

```cql
user has shown interest in "smartphone"
```

## Building blocks

These are the parts that make up an event expression:

- `event`: [`Event`](/reference/cql/expressions/events/event-types)

  The specific [event type](/reference/cql/expressions/events/event-types) to check for.

- `criteria`: [`Criteria`](/reference/cql/expressions/events/criteria/overview) (optional)

  Conditions that further refine which events qualify.

- `quantifier`: [`Quantifier`](/reference/cql/expressions/events/quantifier) (optional)

  The number of times the event must have occurred.

- `window`: [`TimeWindow`](/reference/cql/expressions/events/time-window) (optional)

  The period during which the event must have occurred.

## Event types

These are the available event types you can use in your expressions:

| Expression                                       | Event type                                                                           |
| ------------------------------------------------ | ------------------------------------------------------------------------------------ |
| `user has abandoned a cart`                      | [Cart abandoned](/reference/cql/expressions/events/event-types/cart-abandoned)       |
| `user has abandoned a product`                   | [Product abandoned](/reference/cql/expressions/events/event-types/product-abandoned) |
| `user has become a lead`                         | [Lead generated](/reference/cql/expressions/events/event-types/lead-generated)       |
| `user has completed goal /*<goal-id>*/`          | [Goal completed](/reference/cql/expressions/events/event-types/goal-completed)       |
| `user has experienced a custom event /*<name>*/` | [Event experienced](/reference/cql/expressions/events/event-types/event-experienced) |
| `user has matched audience`                      | [Matched audience](/reference/cql/expressions/events/event-types/audience-matched)   |
| `user has opened a link`                         | [Link opened](/reference/cql/expressions/events/event-types/link-opened)             |
| `user has ordered a product`                     | [Product ordered](/reference/cql/expressions/events/event-types/product-ordered)     |
| `user has placed an order`                       | [Order placed](/reference/cql/expressions/events/event-types/order-placed)           |
| `user has shown interest in /*<topics>*/`        | [Interest shown](/reference/cql/expressions/events/event-types/interest-shown)       |
| `user has signed in`                             | [Signed in](/reference/cql/expressions/events/event-types/signed-in)                 |
| `user has signed up`                             | [Signed up](/reference/cql/expressions/events/event-types/signed-up)                 |
| `user has viewed a campaign`                     | [Campaign viewed](/reference/cql/expressions/events/event-types/campaign-viewed)     |
| `user has viewed a page`                         | [Page viewed](/reference/cql/expressions/events/event-types/page-viewed)             |
| `user has viewed a post`                         | [Post viewed](/reference/cql/expressions/events/event-types/post-viewed)             |
| `user has viewed a product`                      | [Product viewed](/reference/cql/expressions/events/event-types/product-viewed)       |

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