My talk from Northern Voice 2013. There's an app to track nearly everything about ourselves: the calories we consume and burn, every penny we spend, the hours we sleep, every song we listen to--the list goes on and on. Why are we compulsive counters of ourselves and our lives? Over the past fifteen years, technology has enabled us to document and quantify nearly every aspects of our day-to-day existence. And the Internet has enabled us to share it and discover fellow self-trackers. This talk explores how and why an increasing number of people practice self quantification or 'sousveillance': Why do we track our lives this way? Does looking at this data change our behaviour? Why, having assembled the data, do we share it? Why would gathering all this data be a bad idea? Can we truly know ourselves through this practice? You'll leave this talk either inspired to start tracking your trips to the bathroom, or deeply unnerved by those who do.