When I produced the Lectures on Physics, some thirty years ago now, I saw them as an aid to students who were intending to go into physics. I also lamented the difficulties of cramming several hundred years' worth of science into just three volumes. With these Lectures on Computation, matters are somewhat easier, but only just. Firstly, the lectures are not aimed solely at students in computer science, which liberates me from the shackles of exam syllabuses and allows me to cover areas of the subject for no more reason than that they are interesting. Secondly, computer science is not as old as physics; it lags by a couple of hundred years. However, this does not mean that there is significantly less on the computer scientist's plate than on the physicist's: younger it may be, but it has had a far more intense upbringing! So there is still plenty for us to cover.