---
title: Query Engine | LlamaIndex OSS Documentation
---

## Concept

Query engine is a generic interface that allows you to ask question over your data.

A query engine takes in a natural language query, and returns a rich response. It is most often (but not always) built on one or many [indexes](/python/framework/module_guides/indexing/index.md) via [retrievers](/python/framework/module_guides/querying/retriever/index.md). You can compose multiple query engines to achieve more advanced capability.

Tip

If you want to have a conversation with your data (multiple back-and-forth instead of a single question & answer), take a look at [Chat Engine](/python/framework/module_guides/deploying/chat_engines/index.md)

## Usage Pattern

Get started with:

```
query_engine = index.as_query_engine()
response = query_engine.query("Who is Paul Graham.")
```

To stream response:

```
query_engine = index.as_query_engine(streaming=True)
streaming_response = query_engine.query("Who is Paul Graham.")
streaming_response.print_response_stream()
```

See the full [usage pattern](/python/framework/module_guides/deploying/query_engine/usage_pattern/index.md) for more details.

## Modules

Find all the modules in the [modules guide](/python/framework/module_guides/deploying/query_engine/modules/index.md).

## Supporting Modules

There are also [supporting modules](/python/framework/module_guides/deploying/query_engine/supporting_modules/index.md).