This dissertation investigates second language (L2) learners' comprehension of conversational implicatures that arise in two speech acts, requests and refusals. The review of empirical studies that investigated L2 pragmatic comprehension revealed two recurring issues: (a) the lack of a clear definition of conventionality, leaving open the possibility of another factor that affects L2 learners' comprehension, specifically type of speech act (Taguchi, 2005, 2008a,2008b, 2009); and (b) the dominant use of multiple-choice questions that lack task authenticity(Culpeper, Mackey, Taguchi, 2018). In response to these issues, the current study examines the effects of degree of conventionality and type of speech act on L2 learners' comprehension of conversational implicature by comparing L2 learners' comprehension difficulty observed in four groups: (a) conventionally indirect requests, (b) hints, (c) indirect refusals with adjuncts, and (d)indirect refusals without adjuncts. In an effort to increase task authenticity, conversational implicature was measured with two data sets: (a) an immediate, oral response to the preceding turn that contained conversational implicature; and (b) the description of the speaker's intent. Following the concept of an adjacency pair (Schegloff & Sacks, 1973), an L2 learner's response to the preceding turn was expected to show their comprehension; however, an additional collection of interpretations was necessary since various factors, such as L2 learners' speaking and listening skills, and the context where conversational implicatures arise, potentially affect the relationship between responses and interpretations. Thus, this study first investigates the factors that affect L2 learners' ability to respond to or interpret conversational implicatures in requests and refusals, and then examines the extent to which responses correspond to interpretations. Fifty native speakers (NS) and 150 L2 English learners recruited from the large public university and local ESL programs in the American Midwest participated in this study. L2 English learners' language proficiency was measured with the practice TOEFLIBT speaking and listening tests. In order to measure pragmatic comprehension, an oral Discourse Complete Task (DCT) with interpretation was developed. In this task, participants first watched a short videoclip that contained conversational implicatures selected from authentic scripted language samples and responded to the speaker within 10 seconds. After producing oral responses, they were asked to write the speaker's intent. The oral responses and written interpretations were analyzed to show the pattern of how L2 learners responded to and described the interpretations of the preceding turn. Additionally, the oral responses and written interpretations were compared with each other to reveal the relationship between them. The pragmatic analyses were followed by statistical analyses. The statistical analyses were performed with multiple logistic regression and mixed-effects logistic regression models. These analyses found that L2 learners' speaking and listening skills made a significant contribution to the production of relevant responses and appropriate interpretations. Unlike these two factors, degree of conventionality and type of speech act did not significantly affect L2 learners' comprehension of conversational implicature. Lastly, the occurrence of matched cases-- where responses corresponded to interpretations-- depended on L2 learners' speaking and listening skills, and degree of directness. That is, matched cases were more likely to occur when L2 learners responded to direct speech acts than indirect speech acts. When L2 learners responded to indirect speech acts, degree of conventionality and type of speech act did not play a significant role in eliciting matched cases from them. In addition, the responses elicited from higher-level learners reflected their interpretations more closely than those produced by lower-level learners. [The dissertation citations contained here are published with the permission of ProQuest LLC. Further reproduction is prohibited without permission. Copies of dissertations may be obtained by Telephone (800) 1-800-521-0600. Web page: http://bibliotheek.ehb.be:2222/en-US/products/dissertations/individuals.shtml.]