Em inglês, o apóstrofo (apostrophe) usa-se:
1 Em formas possessivas:

This is John's house.
These are the boys' bicycles.
Para mais exemplos, veja possessive case
2 Em formas contraídas:
  • verbos:

    I'll see you tomorrow.
    He doesn't like coffee.

  • Datas:

    John was born in '97.
    They met in the summer of '92.
  • Horas:

    See you at 7 o'clock.
  • Dialectos (por ex. h mudo):

    When 'e arrived 'ome, 'is wife kissed 'im.
3 em certos plurais:
  • Letras:

    How many c's and m's are there in accommodation?
  • Números:

    Life was hard in the 1920's.
    The way you write, your 7's look like 1's.
  • Palavras:

    You have seven and's in this sentence. There are too many!
  • Abreviaturas:

    John met two VIP's yesterday. (1)
    How many MP's do you know personally? (2)

    (1) VIP = very important person
    (2) MP = Member of Parliament