The current study investigated the hypothesis that cognates (i.e., translation equivalents that overlap in form, e.g., "lemon" is "limón" in Spanish) facilitate language switches. Spanish-English bilinguals were cued to switch languages while repeatedly naming pictures with cognate versus noncognate names in separate (Experiment 1) or mixed (Experiments 2 and 3) blocks. In all 3 experiments, on the first presentation of each picture, cognates elicited significantly smaller switch costs and were produced faster than noncognates only on switch trials. However, cognate switch-facilitation effects were eliminated (Experiment 2) or reversed (i.e., larger switch costs for cognates than noncognates, in Experiment 3) in mixed blocks with the repeated presentation of a stimulus, largely because of the increasingly slower responses for cognates on switch trials. Cognates may facilitate switches because of increased dual-language activation, which is inhibited on nonswitch trials. With repeated presentation of the same pictures, dual-language activation may feed backup to the lexical level, increasing competition for selection. In contrast, when naming pictures in a cognate block, bilinguals may avoid discrimination problems at the lexical level by adaptively focusing less on activation at the phonological level. Cross-language overlap in phonology appears to influence language selection at both the phonological and lexical levels, involving multiple cognitive mechanisms and reflecting both automatic processes and rapid adaptation to contextual variations in the extent of dual-language activation.