Nowadays, nearly all style guides suggest the usage of one space after a period or full stop. However, this has been an ongoing debate for years.

In the era of typewriters, two spaces after a full stop were the norm. It was needed to delineate the beginning of a new sentence because of the monospaced typesetting.

In monospaced fonts, every character, be it "j" or "w", occupies the same space on the screen. As a result, a monospace font always takes more space on the screen than a proportional font. For this reason, two spaces were used after punctuation to indicate a full stop — such as a period, question mark, or exclamation point.

In 2019, the American Psychological Association’s Publication Manual changed their recommendation from two to one space after a period. A year later, Microsoft updated Word to mark two spaces after a period as an error.^[1]