It's easy to send animated GIFs from your iPhone using the Messages app, using the built-in app drawer added in iOS 11. In this tutorial we show how to make use of this feature, and amuse and delight your friends with yawning babies, dancing Pokemon, Taylor Swift doing thumbs up, etc.
(It's also pretty easy to send GIFs over WhatsApp, if that's more your thing.)
Sending GIFs from Messages' built-in selection
Open the Messages app, and either tap the compose icon (a pen in a square) to create a new message or open an existing conversation. Unlike many of the newer features in this app, GIF support is not limited to iMessage conversations with other iOS users; it works in conventional texts too.
At the bottom of the screen you'll see two icons to the left of the message body field (a camera and the capital A for Messages' App Store), and if it's an iMessage a microphone to the right so you can record voice messages. Tap the App Store 'A' and a row of new icons will appear below. The icons that appear will vary depending on which compatible apps you've got on your phone.
Tap the red magnifying glass icon. (If you tap and hold it you'll see that it's labelled #images.) Tap the upward-pointing chevron to slide out the drawer to fullscreen; you can swipe up to scroll through more GIFs. Tap the 'Find images' field at the top to search for something specific.
Once you've found a GIF you like, tap it and after a short pause it will be dropped into a message. (If you're not quite sure, you can tap and hold the GIF instead, to see it blown up to full size; tap it again to go back to the previous page, or tap the arrow to add it to your message.)
Add any text you want, then tap the send arrow. If you change your mind, tap the X at the top-right of the GIF to remove it.
Sending your own GIFs
We've shown how to access the built-in selection of GIFs you can find in Messages. But it's also possible to make your own custom GIFs, based on Live Photos, YouTube videos and more. We have separate articles showing how to make GIFs on Mac, and how to make GIFs on an iPhone. You can find and save GIFs online; and don't forget that if someone sends a GIF to you, you can tap and hold to save that to your Photos app.
As part of the iOS 11 update, Apple added a new Animated folder to Photos, and this is where any GIFs you save will be stored. So to add one of your GIFs to a iMessage or text in the Messages app, you simply have to tap the camera icon, then tap Photos, and find the Animated folder. Tap the GIF you want to send, then confirm by tapping Choose, and it will be dropped into a message ready for sending.