The current study investigated first language (L1) effects on listener judgment of comprehensibility and accentedness in second language (L2) speech. The participants were 45 university-level adult speakers of English from three L1 backgrounds (Chinese, Hindi, Farsi), performing a picture narrative task. Ten native English listeners used continuous sliding scales to evaluate the speakers' audio recordings for comprehensibility and accentedness as well as 10 linguistic variables drawn from the domains of pronunciation, fluency, lexis, grammar, and discourse. Comprehensibility was associated with several linguistic variables (segmentals, prosody, fluency, lexis, grammar), but accentedness was primarily linked to pronunciation (segmentals, word stress, intonation). The relative strength of these associations also varied as a function of the speakers' L1, especially for comprehensibility, with Chinese speakers influenced chiefly by pronunciation variables (segmental errors), Hindi speakers by lexicogrammar variables, and Farsi speakers showing no strong association with any linguistic variable. Results overall suggest that speakers' L1 plays an important role in listener judgments of L2 comprehensibility and that instructors aiming to promote L2 speakers' communicative success may need to expand their teaching targets beyond segmentals to include prosody-, fluency-, and lexicogrammar-based targets.