This document discusses contrasts between English and Indonesian consonants that can cause errors for Indonesian learners of English. It analyzes differences in affricates, fricatives, laterals, semi-vowels, and nasals between the two languages, such as English having affricates and fricatives that are voiced or voiceless while Indonesian only has voiceless ones. It also examines problems with consonant clusters in English which are more complex than in Indonesian. Mastering the differences in consonant production between the two languages can help reduce errors for Indonesian ESL learners.