Cumulative work over the last twenty yea rs has defined the glass-forming reg ions in several M-Si-Al-O-N systems (M = Mg, Ca, Y, Ln) with the resulting crystalline products identified after heat treatment. Glass-forming regions in nitrogen-rich sialon glasses have been recently reported and heat treatment of some of these glasses in the Y-Si-Al-O-N system has been performed. The crystallization of yttrium-containing glasses is particularly sensitive to small variations in composition and heat treatment temperature and in the current work the results of three series are discussed : (1) a single composition, Y15.2Si14.6Al8.7O54.6N6.9 (16 e/oN), treated at 30 degrees C intervals between 875-1410 degrees C; (2) compositions of a constant Y : Si:AI ratio of 3:3:2 and up to 32 e/oN and (3) selected compositions lying on the 28 e/oN plane. Two different sets of crystalline products are found to form above and below 1200 degrees C.