When I learned to program computers more years ago than I care to remember, the hardware that I used literally filled a room. Ten years later, it was possible to build a computer that was small enough and cheap enough to have in your home or on your desk at work. Today, we think nothing of carrying in our pockets computers that are more powerful than the ones that were used back in the “good old days” to run a business or navigate a spacecraft to the moon and back. We use them to schedule our lives, read books, listen to music, send and receive e-mails, and even make phone calls. Over the last 15 or so years, several companies have experimented with the idea of making it possible to wear your phone or personal computing device instead of carrying it in your pocket. By 2014, Samsung, Sony, Motorola, and others had taken this idea to its logical conclusion by developing and marketing a range of —devices that are basically wearable computers packaged as wristwatches—with varying degrees of success. In 2015, Apple released its own wearable computing device called the Apple Watch. It remains to be seen whether the it will be as popular as the company’s other consumer products. If it is, then it represents a major new opportunity for iOS developers to profit by extending their existing applications to work with the Apple Watch and to write new application that make use of its unique features.