In LaTeX, the character ~ inserts a non-breaking space. As a rule of thumb, use ~ in the following situations:

  • between a number and its unit of measure: 1000~miles, 183~billion
  • before each citation (e.g., was shown by Smith~\cite{smith_2020})
  • before the last word of a paragraph to prevent it from being placed on a line by itself, especially if the word is short.

To prevent line breaks in the middle of an equation, place curly brackets “{...}” around the equation. For example ${a \in A}$ will always be displayed on one line, whereas ${a^2 + b^2} = {c^2 + d^2}$ may have a line break at the equal sign but nowhere else.