Over the past several years, Instagram has become a must-have mobile app. At it’s heart it’s a camera app, which is one of the most crowded spaces in today’s app landscape. It’s also a social app. Social has such a high barrier to entry that even Google has struggled to scale that wall. So how did Instagram manage to separate itself from the masses, and become a standout app?

There are many reasons why, but in the end they all come back to one overarching theme: Simplicity.

The theory that simpler is better is nothing new. I don’t know that I have ever been part of a project where simplicity wasn’t at least part of the goal. But to actually achieve that goal is a very rare thing. Simplicity actually means sacrifice. It means saying no, and cutting features, and recognizing that you can not make everyone happy all the time. Instagram has embraced simplicity time and again, and I believe that is truly the differentiator that makes it shine. Let’s take a closer look at five ways that Instagram embraced simplicity.

1. Single Platform. Mobile First.

When Instagram was initially rolled out it was iOS only. No Desktop. No Android. No Blackberry. That’s a difficult decision for a business to make. Instagram turned their back on half of their potential customer base, which is a huge risk for any product to take. Why was it the right decision? Because it allowed them to focus all of their efforts on a single platform, with no compromises. They could take full advantage of the benefits of iOS without having to worry about how they’d handle it elsewhere. It also meant that by the time they were ready to expand that strategy to multiple platforms, they had a better idea of what worked and what didn’t. Today they support a variety of platforms, but their desktop presence is still minimal. They recognize that their time and effort is better spent on mobile, so that is what they do.

2. A Minimal Feature Set 

The first version of Instagram wasn’t Instagram. It started out as an app prototype called Burbn. Burbn had a camera component, but it also had a lot of other features including a Foursquare inspired check in service, and a points based game experience. When it came time to transform Burbn into the Instagram we have come to know and love, it meant stripping out a lot of features, and tossing a lot of work. That’s a hard choice, but it allowed them to focus solely on creating the best possible camera functionality. Instagram didn’t include videos, or profiles, or direct messages when it launched. It was photos only, it had the most basic of privacy settings, and it had a small set of filters that you could use to edit your photos. How was it successful with so few bells and whistles? I think it’s because everything it did, it did well, and everything that wasn’t essential, wasn’t included.

3. Square Photos 

This is something so seemingly small, but so brilliant that I had to call it out as it’s own item. Square photos only. Instagram folded this into their marketing and tone so seamlessly that it appeared to be a cosmetic choice only. Their interface was a play on polaroids. Polaroids are square. Instagrams were therefore square. But it goes so much deeper than that. It meant that they never needed to worry about aspect ratio. They didn’t need to worry about layouts that accommodated images of all sizes. They didn’t need to dynamically calculate image heights so that pictures would always be full width. They didn’t need to worry about app rotation because their design always worked in portrait mode.

4. Simple, Effective Interface 

If you take a look at the Instagram app, one of the first things you’ll notice is the camera button. It’s big and it’s blue, and it’s right in the center. It’s not an accident that it’s conveniently located at the bottom of the screen, in easy reach of your thumb, regardless of whether you’re holding the phone with your right or left hand. Instagram wants you to add photos, and their interface reflects that.

Filters are another way that Instagram kept things simple. They recognized that people want their photos to look good online. They recognized that people don’t want to spend a long time fiddling with adjustment sliders. So they came up with a new way to tackle the problem. Filters let you completely change the look of your photo in one easy tap. It’s such an easy, elegant experience. It’s no surprise that users fell in love with it.

5. The Right Features at the Right Time 

Instagram has a pretty good track record of implementing the right features at the right time. In fact, most of the features that I’ve pointed to, as things they avoided, exist in the app today. The difference is that they didn’t jam all of it in during phase one, and hope that people liked it. They started small, paid attention to how people were using the app, and when they did add things, they did so to address a user need. One of the best examples of this is hashtags. In 2011 they implemented hashtags, and it changed the way people use Instagram, and the way people use hashtags. Being selective and smart about the way they roll out new features means that even as Instagram grows, it continues to be a meaningful, engaging user experience.

Instagram is a wonderful example of what is possible when a team understands what their product is, accepts what it is not, and executes against that with total focus. The app is simple, easy to use, and engaging. That’s what keeps 400 million users coming back month after month.