In social life, the use of language plays a highly significant role in interacting with others. Sociolinguistics is a research domain that centers on the diversity of language varieties and is closely related to natural phenomena such as the ability to speak in two or more languages (bilingualism or multilingualism). This study aims to determine the types of code mixing, identify the word class categories of the mixed words, and seek the most dominant type of code mixing in the novel "London Love Story". The data were taken from the novel "London Love Story" by Tissa Ts and collected using the documentation method. This research employs a qualitative method to analyze the data, and the findings are presented in both formal and informal formats. To analyze code mixing, the theory proposed by Peter Muysken (2000) regarding code mixing usage is applied. The research results indicate that out of 78 collected Indonesian-English code mixing data, it was discovered that 37 data were of the insertion type code mixing, 21 data were of the alternation type code mixing, and 20 data were congruent lexicalization. The mixed word categories vary, such as words (e.g., nouns, adjectives, etc.), phrases (e.g., noun phrases, adverb phrases, etc.), and clauses (e.g., dependent and independent clauses). This study found that insertion code mixing predominates as the type of code mixing in the novel. The characters in the novel frequently insert English words or phrases into their speech, which is in Indonesian, especially when they communicate with friends or colleagues.

Keyword: sociolinguistics, code mixing, bilingual, novel