Problems started a little before 11 a.m. ET, according to Down Detector, and appeared to impact many on the East Coast and in Europe. The company said it managed to fix things about two hours later.
"The issue has been resolved," wrote Snapchat Support on Twitter. "If you're still having trouble, please let us know!"
The hashtag #snapchatdown was trending on Monday as people turned to Twitter to vent and confirm that it wasn't just them. Many people reported getting a "failed to send" or "tap to retry" message.
Snap, which makes the messaging app, didn't say what caused the issue.