This paper analyses elements of the legal process of consent to the donation of ‘spare’ embryos to research, including stem-cell research, and makes a recommendation intended to enhance the quality of that process, including on occasion by guarding against the invalidity of such consent. This is important in its own right and also so as to maximise the reproductive treatment options of couples engaged in in vitro fertilisation (IVF) treatment and to avoid possible harms to them. In Part 1, with reference to qualitative data from three UK IVF clinics, we explore the often delicate and contingent nature of what comes to be, for legal purposes, a ‘spare’ embryo. The way in which an embryo becomes ‘spare’, with its implications for the process of consent to donation to research, is not addressed in the relevant reports relating to or codes of practice governing the donation of embryos to research, which assume an unproblematic notion of the ‘spare’ embryo. Significantly, our analysis demon