In 2015, Android and iOS devices still capture the dominant share of mobile developers' attention. But the gap between the also-rans and at least one of these two leading mobile operating systems (OSes) is shrinking. There are also significant differences in how developers in different geographic regions prioritize the mobile platforms they target. This brief looks at which mobile phone and tablet OSes application development and delivery (AD&D) professionals should target when they build mobile apps in 2016.