The remarkable capacity of mammalian embryos to self-organize is preserved in human pluripotent stem cells (hPSC), which on micropatterned surfaces form 2D gastruloids: spatially organized structures that resemble the human gastrula. Due to their simplicity and reproducibility, these provide a powerful experimental system to quantitatively study the mechanisms of patterning and morphogenesis in early human development. Many questions remain about mesoderm development in the human embryo: it is unclear when cells commit to specific mesodermal lineages, what the sources of extra-embryonic mesoderm are, and what drives mesoderm migration. There are likely significant differences between human and mouse in these aspects of development, necessitating a human model. I will discuss three aspects of mesoderm development into which my lab recently gained insight using 2D gastruloids. 1) We investigated the role of FGF/ERK signaling in primitive streak and nascent mesoderm differentiation and discovered distinct roles for three endogenous FGFs expressed during this process. 2) We discovered that extended culture of 2D gastruloids leads to formation of a spatially patterned mesoderm layer through directed migration. 3) We found two distinct extra-embryonic mesoderm lineages arise, one of which derives from the amniotic ectoderm and is unexpectedly modulated by canonical Wnt5b signaling. Together, these findings reveal unexpected molecular mechanisms and cellular behaviors during human mesoderm development that differ from mouse models, highlighting the value of human-specific model systems.