A key therapeutic approach for the treatment of Type 1 diabetes (T1D) is transplantation of functional islet β-cells. Despite recent advances in generating stem cell-derived glucose-responsive insulin(+) cells, their further maturation to fully functional adult β-cells still remains a daunting task. Conquering this hurdle will require a better understanding of the mechanisms driving maturation of embryonic insulin(+) cells into adult β-cells, and the implementation of that knowledge to improve current differentiation protocols. Here, we will review our current understanding of β-cell maturation, and discuss the contribution of key β-cell transcription factor MafA, to this process. The fundamental importance of MafA in regulating adult β-cell maturation and function indicates that enhancing MafA expression may improve the generation of definitive β-cells for transplantation. Additionally, we suggest that the temporal control of MafA induction at a specific stage of β-cell differentiation will be the next critical challenge for achieving optimum maturation of β-cells.