This paper aims to review the theoretical concept of interlingual interference of the mother tongue, Thai to the target language, English and intralingual interference found in EFL student writing in Thai context with the attempt to define the existence of errors according to their sources. This review article also exemplifies some frequent errors normally found in Thai student writing based on three perspectives of interlingual interference; lexical, syntactic and discourse interference and seven aspects of intralingual interference; false analogy, misanalysis, incomplete rule application, exploiting redundancy, overlooking cooccurrence restrictions, hypercorrection and overgeneralization. The pedagogical implication for EFL context is also discussed.