A key design consideration in advanced highs strength steels is to take advantage of the transformation-induced plasticity (TRIP) effect arising from the deformation-induced martensitic transformation of metastable austenite, which is strongly related to the austenite mechanical stability. This thesis investigates how the austenite mechanical stability, in the context of the third generation advanced high strength steels, is affected by its size, shape and surrounding phases using coupled microscopic digital image correlation (micro-DIC) and quasi in-situ (electron backscattered diffraction) EBSD testing. The outcomes contribute to a deeper understanding of the TRIP effect and are beneficial to future high-strength steel designs.