#PrayForParis, One Direction and More: Twitter’s Biggest Moments of 2015

Twitter has collected the trends and viral hits of 2015 — both the happy moments and the sad ones. It was a big year for social change, landmark political decisions — and One Direction. Here are some highlights from the social network's lists of the top hashtags and tweets.

  • #PrayForParis and #JeSuisCharlie amassed millions of tweets from enemies of terrorism worldwide after both of the deadly tragedies in the French capital.
  • #BlackLivesMatter helped unify separate discussions decrying racism and police brutality.
  • Marriage equality legislation was celebrated in the U.S. with #LoveWins and in Ireland with #HomeToVote. President Barack Obama's tweet supporting the Supreme Court's ruling declaring same-sex marriage legal across all states was also retweeted nearly half a million times.
  • #RefugeesWelcome showed people fleeing conflicts and genocide that they had a home waiting in Europe.
  • After 14-year-old Ahmed Mohammed was cuffed when teachers thought his homemade clock was a bomb, 370,000 people tweeted to say #IStandWithAhmed.
  • One Direction's members each produced hundreds of thousands of retweets and favorites as they celebrated five years together and parted ways with member Zayn Malik.
Harry Styles tweet tops Twitter’s moments of 2015 0:51
  • The Women's World Cup attracted plenty of attention, with related tweets garnering 9 billion views.
  • Millions of miles away, the New Horizons probe capped a 9-year journey with its successful #PlutoFlyBy.
  • Caitlyn Jenner collected a million followers in just four hours, breaking a record set by President Obama.
  • And who could forget the colorful debate over #TheDress?

The rest of the year's most memorable or retweetable moments can be found at Twitter's 2015 trends page.