Multiword Expressions (MWEs) are crucial aspects of language use. Second language (L2) learners need to master these MWEs to be able to communicate effectively. In addition, mastering these MWEs helps L2 learners improve their cognitive processing of language input. In this study, my primary objectives were to explore the effectiveness of using Textual Enhancement (TE) to assist L2 speakers’ comprehension of MWEs, to explore whether there is a difference in comprehension between collocations and idioms, and finally, to explore how L2 speakers transact the MWEs’ meanings as presented in texts. While several researchers have explored how input enhancement in general helps L2 learners to learn collocations and idioms for productive use (e.g., Boers et al., 2017; Pam & Karimi, 2016), my focus in this study was to understand and explain in depth how the technique of TE helps L2 learners comprehend MWEs. I included in this study two types of MWEs: collocations and idioms. I also studied the differences in the comprehension between these two types to further understand the transparency factors in the comprehension process. I employed an explanatory sequential mixed methods design in which I used experimental quantitative methods and qualitative methods in one study. In phase one, I started with the experimental part and followed with the qualitative analysis to explain in depth the outcomes of the experimental part. In the qualitative section, I followed an explanatory descriptive case study approach to obtain a deeper understanding of how the participants transacted the meanings of the MWEs. A total of 26 adult Arabic-speaking students in a major Southeastern university in the United States of America volunteered to take part in this study. I collected data through: (1) a reading proficiency test, and (2) a brief survey to gather background information, self-evaluation of language proficiency, and previous experiences with MWEs. In the experimental part, I presented 20 paragraphs derived from online newspaper and magazine articles. Each paragraph contained a collocation or an idiom. Following each paragraph, I presented multiple-choice questions to measure the comprehension of the MWE in the paragraph and an open-ended question for the participants to describe how they had comprehended the MWE. I divided the participants into control and experimental groups in which the MWEs were textually enhanced in the experimental group using bolding, italicization, and highlighting. The results of the study demonstrated TE was effective in assisting the participants to comprehend idioms. In contrast, TE did not show a significant effect in leading the participants to comprehend the collocations. The qualitative data analysis showed the participants used contextual factors, guessing, constituents of the MWEs, and similarities of the MWEs with the first language (L1) as the major strategies to comprehend the MWEs meanings with different degrees between both groups.