Technological prospects of metal nanoparticles (NPs) have stimulated intense research activities into their growth mechanisms to predict shape, size, and crystallinity. Of high interest are low-symmetry nanocrystals (NCs), which exhibit high-energy facets that are relevant in catalysis or plasmonic properties that are attractive for applications in areas such as biomedicine. As a rule of thumb, single-crystal seeds can evolve into either single-crystal NCs or twinned NPs; twinned seeds lead only to twinned products. The main limitation of the seeded-growth method is the structural instability of the seeds, which can spontaneously ripen, even at room temperature after a few hours. However, controlled thermal treatment of the seeds can lead to uniform growth (to ~6 nm) with simultaneous emergence of twin defects. Although the chemistry involved in NC growth appears rather simple, determining the growth mechanisms and reaching predictive synthesis at the nanoscale will require the development of advanced imaging techniques and thorough theoretical modeling.