Use a period [ . ] at the end of a sentence that makes a statement. There is no space between the last letter and the period. Use one space between the period and the first letter of the next sentence.

Use a period at the end of a command.

  • Hand in the poster essays no later than noon on Friday.
  • In case of tremors, leave the building immediately.

Use a period at the end of an indirect question.

  • The teacher asked why Maria had left out the easy exercises.
  • My father used to wonder why Egbert’s ears were so big.

Use a period with abbreviations:

  • Dr. Espinoza arrived from Washington, D.C., at 6 p.m.

Notice that when the period ending the abbreviation comes at the end of a sentence, it will also suffice to end the sentence. On the other hand, when an abbreviation ends a question or exclamation, it is appropriate to add a question mark or exclamation mark after the abbreviation-ending period:

  • Did you enjoy living in Washington, D.C.?

Occasionally, a statement will end with a question or a question will be embedded within a statement. When that happens, it is appropriate to end the sentence with a question mark.

  • We can get to Toronto quicker, can’t we, if we take the 401?
  • His question was, can we end this statement with a question mark?
  • She ended her remarks with a resounding why not?


Acronyms, Abbreviations, and Periods

Acronyms (abbreviations [usually made up of the first letter from a series of words] which we pronounce as words, not a series of letters) usually do not require periods: NATO, LASER, SCUBA, RADAR. Abbreviations (that we pronounce by spelling out the letters) may or may not use periods and you will have to use a dictionary to be sure: FBI, NCC, U.S.A., U.N.I.C.E.F., etc.