I am devastated by the news that Bill Lawvere passed away yesterday. Truly, we have lost one of the giants of our subject. I imagine everyone on this list will have their own special memories of him; here are a few of mine. It was fifty years ago this month that I first corresponded with Bill, sending him the first draft of my paper `The associated sheaf functor in an elementary topos' (which he accepted for publication in JPAA). I still have the reply he sent me: re-reading it brought tears to my eyes as I remembered the very considerable trouble he had taken to help and encourage a young author who was then totally unknown to him, by giving me excellent advice on how to sharpen the presentation of the paper. We met a few months later, at the Aarhus Open House in May 1973; it was there that I aroused Bill's anger by presuming to give a talk about John Conway's theory of numbers and games, which Bill thought (wrongly) to be antithetical to his very strong political views. But the storm passed, and Bill remained a staunch supporter of my work (though I could always rely on him for frank criticism of any imperfections in it). When, in September 2004, Jiri Adamek suggested to a group of senior category-theorists that there was a need for a `steering committee' to ensure the continued smooth running of international CT conferences, there was lengthy discussion about almost every aspect of his proposal; but one thing which nobody queried was his suggestion that Bill should be invited to chair the committee. Happily, Bill accepted the invitation (on condition that I should agree to be the secretary), and he provided us with wise and thoughtful guidance until he stepped down in 2010. The organizers of the 2007 CT meeting in Carvoeiro decided to make the celebration of Bill's 70th birthday a theme of the conference, and they invited me to give a laudatory talk summarizing Bill's mathematical achievements. It was an invitation I accepted with considerable trepidation, and even 24 hours before the talk was due I was unsure how I was going to do justice to all aspects of Bill's work. But in the event it went well, and Bill approved of it; he was particularly amused that I'd included a quote from Karl Marx on one of my slides (he thought, incorrectly, that I hadn't been aware of its source). But there's no need for me to recall anything I said in that talk; Bill himself did the job of summarizing his work much better, in an interview with the Coimbra mathematicians which is available online. Reading it again today, I'm struck once more by the extraordinary mathematical mind of a man I've been privileged to know for almost fifty years. RIP Bill; we'll all miss you. Peter Johnstone [For admin and other information see: http://www.mta.ca/~cat-dist/ ]