Serifs are the small finishing strokes on the ends of letters. Sans serif fonts leave them off. That single difference changes texture, tone and, in some situations, legibility.
What each one does well
Serif faces such as Libre Baskerville or Lora create a strong horizontal rhythm in long paragraphs, which is why books and newspapers have used them for centuries. Sans serif faces such as Work Sans or DM Sans keep their shape at small sizes and low resolutions, which is why interfaces and signage lean on them.
The readability question
The old claim that serifs are always easier to read in print does not hold up well in controlled studies. Size, line length, line spacing, contrast and how familiar the reader is with the typeface matter more than the presence of serifs. A well-set sans at a comfortable size beats a cramped serif every time.
Where the real constraints are
- Small sizes on screen: favour a face with a large x-height and open apertures. Delicate serifs disappear.
- Long-form reading: either works. Get the measure right - 60 to 80 characters per line - before worrying about classification.
- Display sizes: serifs shine. High-contrast faces such as Playfair Display only show their detail large.
- Data and tables: a sans with tabular figures beats a serif with old-style figures.
Tone
Serifs read as established, editorial and formal; sans serifs as direct, current and technical. Neither is a rule. A geometric sans can feel just as period-specific as a serif, and a modern serif can feel sharper than any grotesque.
Using both
Pairing a serif headline with a sans body, or the reverse, is a reliable structure because the contrast is obvious to a reader without being loud. Keep the pairing to two families and let size and weight do the rest of the work.
Try before you decide
Type your real headline into the preview box on any font page. Numbers, capitals and punctuation are where the decision is usually made, and a generic sample sentence hides all three. Start from serif fonts or sans serif fonts.