Discussions concerning a proposed merger between the London Mathematical Society and the Institute of Mathematics and its Applications are at a fairly advanced stage. Details can be found here. A series of meetings has taken place round the UK, and the project is taking on a feel of inevitability. I am still trying to work out what I think about it, but my natural instinct would be against it. At the very least, I hope that LMS members will not vote for it just because they assume that those who are calling for it and have put a great deal of work into it must be right. The purpose of this brief post is not to discuss the merits or otherwise of the idea, but just to draw attention to the fact that there are some who oppose it: their arguments should be carefully considered. If you want to consider them then you might like to look at a blog that has been started by some LMS council members, where some of these arguments are set out. Even if you are not a member of the LMS, comments would be welcome. That is particularly true if you have relevant experience of other mathematical societies.