It is well known that the time course of lexical access is shaped by the number and nature of potential competitor items in the lexicon. While research has outlined the macrostructure of lexical processing (eg, that during spoken word recognition, lexical candidates similar to the input are activated and compete for recognition), many questions remain about the microstructure (how exactly is the competitor set defined?) and dynamics (what is the time course of lexical competition?) of lexical processing, as well as their development as words are learned. Here, we begin to address these issues with a study in which participants learned to recognize words from a lexicon of novel names associated with novel shapes. Each item in the lexicon (eg,/pibo/) had two potential competitors (eg,/pibu/and/dibo/). Half of the words were presented more frequently than the other half during training. This allowed us to examine the development of competition effects with experience. An eye tracker provided an on-line measure of the items being considered for recognition. The results indicate that lexical competition effects among newly-learned items develop quickly.