Add the following to your config.js file for CKEditor:

config.enterMode = CKEDITOR.ENTER_BR;

Example:

...

CKEDITOR.editorConfig = function (config)
{
    config.enterMode = CKEDITOR.ENTER_BR;

    ...
};

Details

The configuration setting that controls this behavior is based on what you want to happen when the user presses Enter.

Just in case someone who’s new to working with HTML reads this, I’m including some basic explanation of the concepts involved and why a tag will need to be inserted when the Enter key is pressed.

We know that if we enter some text into an HTML document and then put additional text on a new line, the browser won’t display the text as two lines, it will ignore any carriage returns and will condense multiple spaces between characters to a single space.

The following HTML:

qwer
tyui

Will be rendered as:

qwer tyui

So the editor needs to insert an HTML tag to tell the browser that it should display the second group of text on a new line.

The configuration setting that controls this is config.enterMode and it offers three options:

1 – Insert paragraph

The default setting creates a paragraph element each time Enter is pressed:

config.enterMode = CKEDITOR.ENTER_P; // inserts `<p>...</p>`

2 – Insert ‘div’

You can choose to create a div element instead of a paragraph:

config.enterMode = CKEDITOR.ENTER_DIV; // inserts `<div></div>`

3 – Insert break (the setting you’re looking for)

If you prefer to not wrap the text in anything, you can choose to insert a line break tag:

config.enterMode = CKEDITOR.ENTER_BR; // inserts `<br />`

The CKEditor documentation indicates that using the ENTER_BR setting is not recommended:

Note: It is recommended to use the CKEDITOR.ENTER_P setting because of its semantic value and correctness. The editor is optimized for this setting.

Another related setting ‘autoParagraph’

There is a second setting that controls a similar situation –config.autoParagraph. How it functions depends on the config.enterMode setting discussed above.

autoParagraph determines whether inline elements such as span are wrapped in the block element (p or div) specified by the enterMode setting. The default is to wrap inline elements, so if you enter a span like this (as HTML):

<span>asdfg</span>

It will be wrapped in a p or div element like this:

<p><span>asdfg</span></p>

or this:

<div><span>asdfg</span></div>

The inline element won’t be wrapped if you set this to false or if you set enterMode to CKEDITOR.ENTER_BR.

The CKEditor documentation includes this note about config.autoParagraph:

Note: Changing the default value might introduce unpredictable usability issues.

Even more settings

There are three more settings that are somewhat related to this subject:

• config.fillEmptyBlocks
• config.forceEnterMode
• config.ignoreEmptyParagraph

Reference

A complete list of the available configuration options can be found here:

• CKEDITOR.config – CKEditor 3 JavaScript API Documentation
• CKEDITOR.config – CKEditor 4 Documentation