WriteLaTeX is an online collaborative editor for writing scientific documents, like papers and theses. It started as idea and a hodgepodge of scripts I wrote as a PhD student. Now we’re a high growth, venture-backed startup and social enterprise, with hundreds of thousands of users around the world. I’ll talk first about writeLaTeX and how you can use it in your work, then about our startup story, and finally about some of the technical challenges we face in bringing a 30-year old technology (TeX) online and in scaling up (e.g. I’ll mention Docker, Ruby on Rails, data protection, cloud services, and bugs, lots of bugs).