Explosive growth in take-up of smartphones and tablets means that the effective size of the internet will increase by several multiples within the next few years. This transformation in scale comes with a major change in character and operating dynamics, creating new opportunities and revenue streams. Twitter is unique amongst social apps: it gives new users a blank canvas in which they can (and must) create their own social network reflecting their own interests, hence building an ‘Interest Graph’, but onboarding new users remains a challenge. Revenue at Twitter is now on a $600 million annual run-rate, scaling rapidly since the introduction of ‘native ads’, and seems set for further growth: the key question is whether it can achieve breakout user growth and mass market scale.