Stoichiometric lithium disilicate glasses were doped with up to 3 mol% CeO2 or Y2O3 and the nucleation and crystal growth kinetics were determined as a function of temperature using in situ hot-stage microscopy. The additives led to a decrease of the steady-state nucleation rates by up to two orders of magnitude and a remarkable increase of the induction time. Moreover, the crystal growth velocities are notably decreased, while the activation energy for crystal growth increases. The cerium-containing samples were analyzed by fluorescence microscopy and spectroscopy, scanning electron microscopy as well as cathodoluminescence measurements. The lithium disilicate crystals consist of fine lamellae separated from each other by a cerium-enriched residual glassy matrix and the crystallization front is enriched by the added oxide. As a result, CeO2 and Y2O3 act as nucleation inhibitors in lithium disilicate glass.