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Can we make a placenta in the Petri dish?

In this issue, we introduce what we hope will become a series of highly topical and, in some instances, controversial debate articles. Our idea is to promote constructive discussion of arguments both ‘for’ and ‘against’ particular research concepts, and so foster and direct future research endeavors that will shed light into new and exciting areas of reproductive biology. The first Debate in this series could not be more appropriate, as it deals with the highly controversial topic of differentiation of human embryonic stem cells (hESC) into trophoblast cells. The contributors, led by R Michael Roberts and Roger Pedersen, are the leading researchers in this field. In this issue they present a detailed account of the evidence both for and against this biological concept (Roberts et al. 2014). There is great interest in both the scientific and medical communities in determining whether hESC can differentiate into a functional trophoblast, as this may lead to the development of in vitro models of placentation. In turn, this could be used to improve our understanding of placental dysfunctions such as pre-eclampsia (Ezashi et al. 2012). However, it is