Force-quitting shouldn't be an all-the-time thing, but can occasionally help when something goes wrong.
Some apps—especially the Facebook, Skypes, and big media apps of the world—don't always behave well on iPhone, iPod touch, or iPad. When and if that happens, you can try "force quitting" them. iOS 9 almost always handles pausing and shutting down apps just fine. So, force quitting isn't something you should do often, because re-launching it again from scratch will consume more power and take more time as it updates in the foreground, but it is something you should know how to do for when you need it.
How to force quit an app on iPhone or iPad
While the design of iOS 9's fast app switcher and task manager has changed, the way it works is the same as iOS 7 and iOS 8.
- Double click the Home button (or 3D Touch press the left side of the screen on iPhone 6s) to bring up the fast app switcher.
- Swipe to the app you want to force quit.
Touch the app card and flick it up and off the screen

I'll confess to force-quitting Facebook and Skype semi-regularly. That's because, historically, they've been offensively bad at power management. I used to force-quit Maps and Google Maps after turn-by-turn navigation but they've both gotten much better at powering down over the last year or two.
How to force quit three apps at once on iPhone or iPad
You almost never want to kill more than one app at a time. It will inevitably decrease performance and battery life since you're killing state and forcing everything to start over. If you can't find the source of a rogue process or are otherwise pressed for time and just need everything to stop, however, it's again something you should know how to do. Even if you don't ever do it.
- Double click the Home button (or 3D Touch press the left side of the screen on iPhone 6s) to bring up the fast app switcher.
- Swipe to the apps you want to force quit—up to three at a time.
Touch the app cards all at the same time and flick them up and off the screen.

Because iOS 9 shows a fourth, blurred out, app all the way to the left, you can try and do four at a time. I can't say I've gotten it to work, but I will say I keep trying. Sometimes.
How to force quit an app without using the fast app switcher
If for some reason you don't want to use the fast app switcher interface to kill an app, you can still use the old fashioned way. (Which you might be familiar with from the Apple Watch.)
- Go to the app you want to force quit.
- Hold down the On/Off button until the "slide to power off" screen appears.
- Hold down the Home button until you're dropped back onto the Home screen.

There's a subtle difference in how the system tracks this version of force quitting, but the result is the same.

Reader comments
How to kill or force quit apps on iOS
I'm so guilty of constantly force quitting apps. I think it's because on android devices swiping an app away is just closing it, not force quitting it. Gotta break the habit.
Sent from the iMore App
I recently started doing this more frequently because lately some apps have been running like crap. This started before iOS 9. I'm using an iPhone 6. So annoying.
Sent from the iMore App
Wtf im force quitting all the time then why should i let apps running on background?
They're not "running" in the background, they're "paused" in the background. Assuming they don't have any background processes going. But assuming it's a good app without bad background processes, you should let your RAM do its job and really only force close an app if it's misbehaving.
Right before I plug in my iPhone to charge overnight, I force quit all apps in the background. So your saying I shouldn't be doing this?
Sent from the iMore App
Do this ONLY when apps go rogue. As indicated by idb closing apps that you use periodically actually uses more battery since they need to be activated from scratch instead on being readily available from your ram.
If those people are concerned of battery life when leaving apps in the app switcher then disable app refresh in backgrounds.
It's not necessarily that it's bad for the phone, it just doesn't do any good either. It's also a common misconception that you should close all your apps to save RAM, but whenever you run out of RAM, iOS automatically closes apps to make room for new ones.
Swiping up from the task switcher is NOT a force quit however the second one mentioned here is.
Sent from the iMore App
Thank you! I was beginning to get highly irritated at everyone claiming they "force" quit all their apps.
Hopefully the writer updates his article since he is confusing the two actions and spreading misinformation.
THIS app, iMore, need update because I have to shut it down often to see comments but there aren't any there.. But they displays in desktop version.
Sent from the iMore App
Great tips! Thanks, Rene!
There seems to be no difference in the steps listed for one app and three apps?
As long as force quitting isn't harming anything I'm not gonna worry about it.
Sent from the iMore App
Multitasking and killing apps in iOS 9 is awful. It was way better in iOS 8.
Why is this called "Force Close"? That same language is used on the Mac (actually Force Exit) for those really daft apps and sometimes Finder when it decides to be a prick. Nonetheless, there isn't any need to keep an app open unless you are work within multiple apps or multiple social media platforms. Having more apps running means more RAM usage, despite background app allocation. Plus, the more apps you have open the more you'll have to filter through to get to the one you want and iOS 9's card stack UI isn't as swift as we wished it would be.
Sent from the iMore App
All of what you said is true if you are talking about OS X. Only *some* of what you said is true when talking about iOS though. For instance backgrounded apps on iOS don't use any CPU cycles or RAM at all, or at least, the RAM they are using is marked for re-allocation and therefore they aren't really "using" it at all.
I've been using the force-touch on the left side of the screen to get at multi-tasking as it's way easier and addictive too. However, it only seems to work properly about 90% of the time. The rest of the time it starts an app or just fails or all the icons start to wiggle etc.
It's certainly handy, but Apple really needs to work out some of the bugs.
This would have to be one of the dumbest post ever! So much so I had create an account to comment.
If you "force close" the app is still running and even so when background services are disabled..
Don't believe me? See for yourself.
Next time you "force close" your apps restart your phone by either powering down or holding the power button and home button simultaneously until after the screen switches off then release when the apple logo appears, once it restarts enter passwords if enabled then double tap the home key again and whalla, the apps you just closed are back.
It's been like that since the iPhone 4 was released from what I can remember so if a simpleton like myself knows this then you the experts writing this story are retarded.
Reason why? Well it's still running for however long they want in your phones memory, because you can't see it or close it doesn't mean it's closed.
good lord, you mean they can't just have an 'X' pop-up after double pressing the home button to close all apps at once??? is that so hard? ghey apple.
hold the home button
Nxt you task the app that you whant