Dynamic high-resolution transmission electron microscopy (DHRTEM) has been used to follow the early events in ammonia/2H-TaS2intercalation. This molecular intercalation process is characterized by two intriguing transient partial gallery expansions of 0.6 and 1.4 Å, prior to and during intercalation, respectively. These expansions do not persist throughout the intercalation process, eventually yielding to full gallery expansions of 3.0 Å. The former partial expansion was observed prior to intercalation during preintercalation ammonia adsorption on the basal planes and can be associated with a charge-transfer-induced host-layer “loosening” of the outermost guest gallery via octahedral-to-trigonal prismatic restacking of the adjacent host layers. The latter expansion is associated with the formation of a near planar ammonia species, which reduces the elastic strain energy for molecular intercalation.