Apple won't release its next-generation iPhone until the fall of 2016, so there are still months of development ahead. For the current time, Apple's flagship iPhones are the iPhone 6s and the iPhone 6s Plus, released to the public in September of 2015.
Though it will be several months before the new iPhone 7 launches, rumors about the device started trickling out in January of 2016. We've already gleaned many details about the upcoming iPhone, giving us some information on what to expect when it debuts.
Since the 3GS launched in 2009, Apple has used an alternating "S" naming formula to mark years where the iPhone does not receive a major redesign, saving its numbered upgrades for years where design changes are introduced. Releases have been as follows:
2007 - iPhone
2008 - iPhone 3G
2009 - iPhone 3GS
2010 - iPhone 4 (new design)
2011 - iPhone 4s
2012 - iPhone 5 (new design)
2013 - iPhone 5s
2014 - iPhone 6 and iPhone 6 Plus (new design)
2015 - iPhone 6s and iPhone 6s Plus
The next-generation iPhone is expected to be called the iPhone 7. 2015 marked an "S" iPhone upgrade year that introduced new features such as an improved camera and a better processor, but 2016 will bring an even-year upgrade that will include a new iPhone design in addition to new features.
Apple will continue releasing two versions of each iPhone, so we can expect to see an iPhone 7 and an iPhone 7 Plus in 2016. Apple is said to be planning to stick to the 4.7- and 5.5-inch screen sizes it first introduced with the iPhone 6 and 6 Plus.
Apple is still working on finalizing the iPhone 7's body so we don't know exactly what it will look like, but multiple rumors suggest it will be a modest update that continues to use a design similar to the design of the iPhone 6s. It is said to have the same general shape as the iPhone 6s, but it may have a camera that protrudes less (though rumors currently disagree on this point). Antenna bands across the back of the device have been removed, but are expected to remain at the top, bottom, and sides of the iPhone.