Em-dashes and spaces

Whether to use spaces around an em dash depends on the style guide being followed; however, the general rule is no spaces, as is common in book publishing and academic style guides like Chicago, MLA, and APA. The major exception is AP style and many newspapers, which require a space on either side of the em dash for readability in narrow columns. 

Consistency is key, so always follow the specific guidelines of your style guide. 

Style guide recommendations

No spaces: Most major academic and book publishers recommend using the em dash without spaces on either side. This is considered standard for most forms of writing.

Example: "The flight—which had already been delayed three times—was canceled."

Spaces around the dash: Newspapers, including those that follow AP style, typically use spaces around an em dash.

Example: "The flight — which had already been delayed three times — was canceled."

Why the difference? The spacing in newspapers improves readability in narrow columns, while the lack of space is often preferred for book publishing to create a more cohesive look. 

Tips for using em dashes with spaces

Be consistent: Whichever style you choose, apply it consistently throughout your document.

Consider context: The most important rule is to follow the style guide you are required to use (e.g., for a specific publication, academic assignment, or newspaper).

Think about a thin space: For even more professional typesetting, a very small "thin space" can be used on each side of an em dash instead of a full space. 

The Problem With Em-dashes

In some langauges, m-dashes are frequently used as punctuation marks. In English they are seldom used. BUT the (over)use of m-dashes is a commonly recognised symptom of a text being written by AI, and for that reason, should be avoided as much as possible in acadmic writing, they create a bad impression. I suggest removing as many as you can replacing them with other punctuation where it is possible.