While the organisation is based in the US, its influence has spread far and wide, with people all over the world marking the day by being kind to one another.
An act of kindness doesn’t have to be a grand gesture. It could be something as small as smiling at a stranger who you would have otherwise ignored, or paying for the coffee for the person in line behind you at your local cafe.
This year, many people have shared what they did to brighten someone else's day on Twitter.
As one person pointed out, being kind to one another on a daily basis doesn't cost a thing.
Here are 12 of the best tweets from Random Acts of Kindness Day 2019:
1. A sweet chocolate treat
2. A belated message of gratitude
3. An annual caffeinated tradition
4. The difference a small act can make
5. If animals can get along, then so can humans
6. The cost of kindness
7. Giving someone the boost they need
8. Taking care of the community
9. A worthy challenge
10. Teamwork makes the dream work
11. A little act of kindness can go a long way
12. Learning how to change your outlook on life
Click here to read about 12 amazing acts of kindness that went viral for the best reasons.
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