This study is a qualitative analysis of coherence problems in middle school English textbooks, with a focus on whether coherence is achieved successfully in the textbook dialogues. To this end, eighteen middle school English textbooks were analyzed on the basis of coherence principles such as clarity, logicality, and informativeness. The results showed that coherence problems exhibited in the textbook dialogues cover lack of clarity, violation of logicality, and violation of the principle of informativeness. The lack of clarity was evident in the textbooks when a vague or general statement was chosen in the situation where a specific statement is appropriate, and when a wrong choice of grammatical items led to semantic ambiguity. The results also revealed different facets of logicality problems: (a) the absence of logical connections between ideas, (b) inconsistent temporal frames, and (c) the illogical order of information structures from a specific statement to a general one, which is the opposite of what is normally sequenced. With respect to the principle of informativeness, two major problems were identified in the textbooks: (a) the presentation of more information than is required and (b) the presentation of less information than is needed. The coherence problems were also found to be attributable to such factors as L1 interference and a disregard of world knowledge. On the basis of the findings, helpful suggestions are provided for curriculum developers to cope adequately with the coherence problems.