By and by is usually an adverb meaning (1) after a while or (2) soon, but it also works as a noun meaning the future. As a noun, by-and-by is often hyphenated to avoid confusion. By the by means incidentally, by the way, or beside the point.
Both might be considered out of place in formal writing. Bye and bye, bye the bye, by the bye, etc. are misspellings.
Examples
These writers use the adverb by and by well:
By and by, a new home was built with Allen spearheading the efforts as construction manager. [The Huntsville Times]
We shall know, by and by, if she has it in her to handle the challenge. [Deccan Chronicle]
By and by, everyone Sam has anything to do with ends up dead, and he stays alive only by the not-so-good graces of MI6 … [Daily Herald]
Here’s an example of the rare noun form, by-and-by, used correctly:
Everybody has so much money that serious negotiations can be deferred into the by-and-by. [New York Times]
And the following are examples of by the by used well:
The song, by the by, is infectious in a get-behind-me-earworm kind of way. [Irish Times]
By the by, why are the doughy guys with big hearts always named Sam in high fantasy? [Houston Chronicle]
Attorney Grieve left the distinct impression, by the by, that he regarded the Press and internet users as impertinent, malign hyenas. [Daily Mail]
