As well as Timothy Gowers (who is, yes, an absolutely first-rate mathematician and a very good expositor too), the PCM has a bunch of contributions from Terry T

As well as Timothy Gowers (who is, yes, an absolutely first-rate mathematician and a very good expositor too), the PCM has a bunch of contributions from Terry Tao (blog at http://terrytao.wordpress.com/ http://terrytao.wordpress.com/; http://terrytao.wordpress.com/?s=princeton+companion+to+mathematics http://terrytao.wordpress.com/?s=princeton+companion+to+math... to find pre-production versions of several of his PCM articles) who is also a Fields Medallist, a very good expositor, and a blogger.