This study examines the putative benefits of explicit phonetic instruction, high variability phonetic training, and their effects on adult nonnative speakers' Mandarin tone productions. Monolingual first language (L1) English speakers (n = 80), intermediate second language (L2) Mandarin learners (n = 40), and L1 Mandarin speakers (n = 40) took part in a multiday Mandarin-like artificial language learning task. Participants were asked to repeat a syllable--tone combination immediately after hearing it. Half of all participants were exposed to speech from 1 talker (low variability) while the other half heard speech from 4 talkers (high variability). Half of the L1 English participants were given daily explicit instruction on Mandarin tone contours, while the other half were not. Tone accuracy was measured by L1 Mandarin raters (n = 104) who classified productions according to their perceived tonal category. Explicit instruction of tone contours facilitated L1 English participants' production of rising and falling tone contours. High variability input alone had no main effect on participants' productions but interacted with explicit instruction to improve participants' productions of high-level tone contours. These results motivate an L2 tone production training approach that consists of explicit tone instruction followed by gradual exposure to more variable speech.