Magnesium alloys are excellent material candidate to reduce mass of automotive structures, and as such to meet the Department of Energy's targets in fuel economy and clean energy. However, magnesium alloys show poor ductility at room temperature, which is one of the most important impediments to achieving cost-effective manufacturing of wrought alloys and insuring good energy absorption in crash structures. This Master thesis aims to identify the mechanisms behind the low ductility of magnesium. Therefore, non-destructive EBSD analyses upon tension of both a strong and weak textured magnesium alloy were conducted with a focus on the role of twinning in fracture initiation. This study revealed five mechanisms responsible for early fracture, all of which relate to twinning activity. These mechanisms were involved directly in the shear incompatibility arising from interactions between twin-twin, twin-slip, twin-grain boundary, and double twinning. Backstress played a major role in twin-grain boundary and twin-twin boundary interactions.