Dive Brief: 

• According to a Business Insider analyst report, Google Glass will sell a million units when it is released next year and will grow to 21 million units sold by 2018. 
• The popularity will be spurred by professionals using the smart eyewear for medical training, scientific discovery and photography, and Business Insider estimates the cost of Glass will fall to $600 within two years, making it even more accessible. 
• Google has already released the Glass Development Kit for app developers to get an early start on the eyewear's mainstream adoption. 

Dive Insight: 

Critics have long had doubts about whether or not Glass would become mainstream enough to make it a worthwhile tool. If 21 million people are using Glass by 2018, that would be a worthwhile investment for marketers to develop apps and format advertising for the wearable device. In particular, B2B marketers looking to reach certain professions — like doctors, scientists and photographers — may want to get a jumpstart on developing for Glass before it hits the mainstream.