This paper reports on the results of an analysis of 80 copyright transfer agreements (CTAs) with particular regard to their effect on author self-archiving. It shows the number of CTAs asking for copyright assignment, the time of assignment and what happens when copyright cannot be assigned. It outlines the warranties required of the author, and the exceptions granted back to the author by which they may use their own work. In particular it focuses on the number of CTAs allowing self-archiving and the conditions under which they may do so. It concludes that whether an author can safely self-archive or not depends on a complex matrix of the following factors: i) whether copyright assignment or a non-exclusive licence is required; ii) the time of copyright assignment; iii) if (and when) CTA’s actually allow self-archiving; iv) if publishers do not allow self-archiving, but do not see it as ‘prior publication’; v) whether the preprint is legally a separate copyright work to the refereed postprint; and vi) whether the author wishes to self-archive a pre-print, postprint or both.