The context of a presentation determines, or should determine, how you approach its preparation. The context includes many things, the audience, the purpose of the presentation, the occasion, what precedes the presentation and what follows from it. It will define what you expect from the audience, and will influence how you prepare yourself for the talk. A simple example. Suppose that you have been invited to give a series of lectures at a summer school. What more do you need to know, other than the topic? Here are a few of the questions that you need to have answered before you can start planning the course. 1. Is it an introductory course aimed at graduate students in their first year, or is it an advanced course more suited to graduates in their final year and young postdoctoral researchers? 2. Are the participants expected to ask questions during the lecture, or wait until the end? 3. Will there be any problem classes or discussion sessions? 4. Will lecture notes be handed out to participants before or after the lecture? 5. Will the proceedings be published, and if so, when? 6. What are the other lecture courses going to cover? 7. Will the basic theory already have been covered, or are they expected to know it already, or should you spend half of the first lecture going over it, just in case some have not seen it before? 8. If it is your job to give the basic introductory lectures, should you follow the standard approach in the usual text books, or should you assume that they have already covered that ground and try to give them more insight into the subject? 9. Will any of the lectures that come later in the school make any assumptions about what they have learned in your lectures? 10. Is there a social programme? If so, are you expected to participate in the activities and discuss the subject informally with the participants (which, from our experience, is always much appreciated), or can you spend most of the time in your room writing the next lecture?