17 February 2016 Last updated at 06:45 GMT
Newsround meets children from all over the world and hears some incredible stories of sibling relationships.
Fabio becomes a big brother for the first time, four identical sisters show us what life is like for them, and Syrian refugee Milad is desperate to see his brother again. Will he get his wish?
Take a look at more of Newsround's special siblings stuff!
They make you laugh, drive you mad... and will be your friend for life - brothers and sisters are among the most important people to us.