You're here because you have an iPhone with no headphone jack and you can no longer directly plug normal headphones into the phone.
Apple used to include a Lighting-to-3.5mm adapter with the new iPhone models but has run out of goodwill and doesn't do that anymore. You might be content with the included Lightning headphones, but you may want to use other wired headphones.
Here's a list for you, then. Apple still sells its adapter, cheekily, but there are other available to allow you to use wired headphones with your jack-less iPhone.
Best Lightning headphone adapters for iPhone 2019
Apple Lightning to 3.5mm Headphone Jack Adapter
This is the Apple adapter that comes in the box, so you may not need another, but then again it is pretty easy to lose. £9 isn't too bad a price for an Apple product, even a tiny one like this. If you want a spare, you shouldn't balk too much at getting this one.
Belkin Lightning Audio + Charge RockStar
This Belkin adapter solves the issue of being able to charge your phone while listening to music using headphones.
Beware, though - this doesn't have a 3.5mm headphone jack (Belkin does offer that as well for £29.99/US$32.94, but we have not tested it), it's just to plug in and charge via Lightning while using the bundled Lightning EarPods. You could always use the bundled Apple adapter to use normal headphones though. But that would be mental. It's also an expensive accessory.
CONMDEX Lightning to 3.5 mm Headphone Jack Adapter
Naturally with small accessories like this, there is already a raft of third-party adapters. Here is one. It does what the Apple one does and costs less (at the time of writing).
FiiO i1 Apple Lightning Amplifier
Apple's decision to ditch ye olde 3.5mm headphone socket on the iPhone 7 continues to cause a fuss even now that we've moved onto this year's new iPhone 8. To be fair, Apple does include a free Lightning-to-3.5mm adapter with the latest iPhones so that you can continue to use your existing headphones with the Lightning connector that replaced the traditional headphone socket.
However, that little adapter isn't just a straightforward bit of cable. It also includes a small chip called a DAC - digital-to-analogue converter - that converts the digital audio from the Lightning connector into analogue sound for your headphones. But, just as the free EarPods that come with the iPhone provide pretty basic sound quality, so that free Lightning-to-3.5mm adapter isn't all that good either.
Apple's adapter has been criticised for poor sound quality, and also for being incompatible with many headphones and headsets. So if you've spent a fair bit of money on some high-quality headphones then it's worthwhile looking for an alternative that provides better sound, such as the FiiO i1.
FiiO is well-known for its range of high-res audio players - iPods on steroids, essentially - and it's brought that hi-fi expertise to the i1. If you're happy listening to music with Apple's cheap and cheerful Earpods then you might not notice too much difference. But, with a decent set of headphones plugged in, you'll notice that the i1 produces a more balanced and natural sound than Apple's little adapter, with a slightly more expansive sound stage that works well with live recordings.
The DAC in the i1 also works with its internal microphone to provide high-quality voice calls as well. Our only complaint is that the 80cm cable is quite long, and can get snagged when you're moving about. However, FiiO designed it that way so that you can leave your iPhone in a pocket or bag to keep it safe, and just use the long cable to connect to your headphones.
Griffin iTrip Clip
This small Bluetooth clip is an excellent way around the headphone conundrum. It works with any headphones with a 3.5mm jack, and wirelessly transmits music from your iPhone 7 or 7 Plus to your ears.
It charges up via the included micro USB cable and will give you between 4-6 hours playback. Pairing with your phone is easy and means you can charge your iPhone while listening to music wirelessly.
It's a good, affordable way to make existing headphones wireless without forking out for Bluetooth headphones.
Bear in mind though that it won't work with the Lightning connector headphones that comes with the iPhone 7 - it also doesn't come with headphone, despite the picture here.