--- - |2 Abstract The present longitudinal study of 83 mother–child dyads (40 girls) assessed how emotional availability (EA) and maternal mental state language (MSL) are related to children's first‐ and second‐order false belief understanding (FBU). EA was measured with the emotional availability scales at 7 and 50 months, maternal MSL within free play at 7 months, and within a book context at 24 months. First‐order FBU was assessed at 50 months and second‐order FBU at 70 months. The results emphasize the specific importance of high emotional connectedness between mother and infant for early and later mother–child conversations about inner states. They also stress the prominent role of maternal cognition MSL for children's first‐ and second‐order FBU. Thereby, maternal cognition MSL seems to mediate the influence of early EA on preschoolers' first‐order FBU. The results are discussed within different theoretical frameworks of FBU development. - Social Development, Volume 27, Issue 4, Page 841-857, November 2018.