What is the difference between 由于 and 因为?
由于 means "due to" or "because of".
因为 means "because".

There are also some differences in usage too,


由于 is usually placed at the beginning of a sentence


  由于天气恶劣，飞机被迫折返梳邦机场降落。 Due to the bad weather, the plane is forced
  to turn back to land at Subang Airport.

因为 can be used where the cause is stated following the effect


  我不需要上学，因为今天是公共假日。 I don't need to go to school because today is a
  public holiday.

因为 can be used in conjunction with 所以


  因为今天是公共假日，所以我不需要上学。 Because today is a public holiday, therefore I
  don't need to go to school.