To see them, simply press and hold on the Reactions button -- it's where the thumbs-up Like button is currently -- select which one you want, and release. If the post has a slew of different reactions to it, you'll see a summary of the three most frequent reaction icons. On the other end, the person receiving them will get notifications saying someone "reacted" to the post.

Introducing Reactions from Facebook on Vimeo.

"People come to Facebook and share all kinds of things," says Sammi Krug, the product manager behind Reactions. "And we kept hearing feedback from people that there wasn't an easy way to express empathy for these different kinds of posts." Zuckerberg in particular took the user feedback to heart and pulled a bunch of people together to start working on a solution about a year or so ago.

From there, the team did a ton of research -- from surveys to analysis of popular stickers -- to figure out just what reactions to add. When they whittled it down to about six, Facebook then began testing it -- you can see we saw a sneak peek of Reactions as early as last October -- in about seven different countries.

"One of the things we really wanted to be careful of, is will this translate well" says Krug. "We wanted these reactions to be globally understood." That's one of the reasons Reactions is launching with just five additional icons instead of the original six that we saw in October. That's because the "Yay" reaction just didn't test well globally and was a little too vague in some markets. The rest, however, proved to be popular enough, with Love being the most popular out of all the new Reactions (The Like button, however, still reigns supreme).

So does that mean we're stuck with the six or so Reactions we have now? Not at all. "Once this actually rolls out, we'll learn more about how people use the feature," says Krug. "We'll continue to iterate it over time, based on user feedback."

Reactions will roll out globally starting today on iOS, Android, the desktop as well as the mobile browser. You'll start to see the change occur over the next couple of days, though bear in mind that you do need to be on the latest version of the Facebook app to get the feature.

Still, we had to ask, why isn't there a "dislike" button instead? "It would have been too binary," says Krug. "This way, though, you'll have more ways to express yourself. That's the goal."