Is Twitter an ephemeral technology, consisting of mundane chat about people's personal lives? Or can a study of its use help us to understand how we express our identities on and offline? Can Twitter be used for professional or academic activity, and should we try to separate our public and private digital personae? This lecture will address such questions, with the aid of slides of 140 characters and live tweets from the audience at UCL and on the internet. Authors: Claire Warwick (UCLDH), @clhw1, Melissa Terras, @melissaterras, #melissaterras (UCLDH); Claire Ross, @clairey_ross (UCLDH); Anne Welsh, @AnneWelsh (UCLDH) This lecture marks the 5th anniversary of Twitter on 21 March.