Study an egg today to make an embryo tomorrow.

When accepting to guest edit this Special Issue, our thoughts went, of course, to our peers who would take advantage of the contributions included, but also to younger researchers and students and to how they would benefit from the use of this Special Issue as an open window to move in depth into some of the most updated advancements in our knowledge of the female gamete. The breathtaking sense of wonder that the female germ cell inspires is well summarised by the renowned phrase of William Harvey ‘Ex ovo omnia’, remarked on in a short black and white film titled ‘In the Beginning’ (http://archive.org/details/IntheBeg1937), a motion picture made by the U.S. Department of Agriculture, Bureau of Dairy Industry, sometime between 1935-1937 that starts, again, with Harvey’s ‘All animals, even the viviparous ones and even man himself, take their origin from eggs’ and continues showing what we believe to be one of the firsts successful attempts to film, with an educational purpose, the gametes during fertilisation and the preimplantation embryos during their segmentation divisions. When the light is switched back, the projection is punctually followed by moments of silence, when we realise that, although almost 80 years have passed since that film was made, our knowledge of mammalian gametes and reproduction has improved very little – though it is a precious little. It is to this "little" that we dedicate this Special Issue.