Background: The health financing systems in low- and middle-income countries mostly rely on out-of-pocket payments. Many of these countries, including Ethiopia are implementing community-based health insurance schemes as an alternative to user fees in reaching the goal of universal health coverage. Apart from a few successful experiences, the schemes face different sustainability issues in the context of most of these countries. In Ethiopia, the sustainability of the scheme and its challenges has not yet well-investigated. Objective: The purpose of the dissertation was to investigate the sustainability of the community- based health insurance schemes and underlying challenges with a focus on the performance of the scheme and the quality of health care in two districts of northeast Ethiopia, Tehulederie and Kallu. Methods: Both quantitative and qualitative research methods were employed to address the objectives of the study. A community-based cross-sectional study was employed to measure membership adherence and perceived quality of care. The study population of interest includes households in selected Kebeles of the two districts who have ever been enrolled in the scheme. A three-stage random sampling was employed to obtain the representative sample for each district to measure the time to drop out of the scheme, the perceived quality of care, and related factors. For the household survey, a pretested structured questionnaire was administered face-to-face to 1232 household heads in the community by trained data collectors. A desk review was conducted to obtain relevant data at the scheme offices and health centers. Additional data on facility-level factors that influence the perceived quality of care were obtained through self-administered questionnaires among 194 health care providers working in 12 health centers. A mixed methods case study was employed to evaluate the performance of the scheme. The databases of the two schemes were reviewed retrospectively using selected key performance indicators to evaluate the trends in membership growth and financial viability. Qualitative data were collected through key informant interviews, in-depth interviews, and informal interviews to explore the underlying challenges that impede membership development efforts and the financial viability of the scheme. The study participants include scheme personnel, district health officers, health facility directors, health care providers, health extension workers, Kebele leaders, and community members. The participants were selected purposively using the maximum variation approach and the sample size for each study district was decided based on the notion of data saturation, with no new information emerging from participants. A total of 28 formal interviews were conducted face-to-face by the principal investigator. Informal interviews were also made during visits to the various setups to capture important information that could be triangulated with the findings of the formal interviews. The relationship between the time to drop out and the explanatory variables was examined using the accelerated failure time shared frailty models by assuming the time to drop out of the scheme is correlated within the clusters (Kebeles), while the relationship between the perceived quality of care and associated factors was assessed using multilevel linear regression model thereby the characteristics of the respondents and health centers were considered as individual and group- level variables respectively. Exploratory factor analysis was performed to assess the validity of the questionnaires designed to measure the perceived quality of care, and some exploratory variables with composite measures, while the reliability of the scales was estimated by measuring the internal consistency using Cronbach’s alpha. To address objectives III and IV, trends for each performance indicator of the schemes were analyzed descriptively for the periods under review. The data from the interviews were audio recorded, transcribed verbatim, and translated into English. Thematic networks analysis was employed with both deductive and inductive coding approaches. Results: In measuring the time to drop out, the total follow-up period was 6816 person-years of observation, with an average follow-up time of 5.53 years (95% CI: 5.38, 5.68). Overall, 29% of the study participants had dropped out of CBHI following their initial enrollment in the scheme with an incidence rate of 5.27 per 100 person-year. The marital status of the respondents, household size, presence of chronic illness, history of hospitalization, higher perceived quality of care, perceived financial risk protection, and higher trust in the scheme management were significantly associated with the time to drop out. Contrary to the literature, wealth status did not show a significant correlation with the time to drop out. Regarding the perceived quality of care, the mean score was 70.28 on a scale of 20-100 with an SD of 8.39. Five dimensions of perceived quality of care were extracted from the factor analysis, with the patient-provider communication dimension having the highest mean score (M = 77.84, SD = 10.12), and information provision having the lowest (M = 64.67, SD = 13.87). Wealth status, current insurance status, perceived health status, presence of chronic illness, and recency of health center visit were individual-level variables that showed a significant association with the perceived quality of care. At the cluster level, the work experience of health care providers, patient volume, and an interaction term between patient volume and staff job satisfaction also showed a significant association. Over the study period (2017 to 2021), enrollment in the scheme at the study districts exhibited non-linear trends with both positive and negative growth rates being identified. Overall, the scheme in Tehulederie has a relatively higher population coverage and better membership retention compared to Kallu, which could be due to the strong foundation laid by a rigorous public awareness campaign and technical support during the pilot phase. The challenges contributing to the observed level of performance in both districts have been summarized under four main themes that include quality of health care, claims reimbursement for insurance holders, governance practices, and community awareness and acceptability of the scheme. Both schemes experienced excess claims costs and negative net income in almost all of the study period. Even after government subsidies, the scheme’s net income remained negative for some reporting periods. Adverse selection, moral hazard behaviors, medicine shortages, delays in service provider claims settlement, and low insurance premiums were the key challenges that have been highlighted as impeding the scheme's financial performance. Conclusion: The study highlighted the importance of considering both individual and cluster level factors linked to people’s membership adherence and the perceived quality of care to enhance the scheme’s performance. The scheme experienced negative growth ratios in both study sites over five years period, showing that it is not functionally viable. The scheme in both districts also spent more than it received for claims settlement in almost all the periods under the study, and experienced heavy losses in these periods, indicating that it is not financially viable. This implies that the scheme could not be able to generate adequate funds to satisfy the health care needs of its members. Overall, the sustainability of the scheme in the study districts is in jeopardy. The scheme will inevitably fail to attain its mission unless relevant stakeholders at all levels of government demonstrate political will and commitment to address the existing implementation challenges, as well as advocate for the community. Keywords: Sustainability, community-based health insurance, membership adherence, perceived quality of care, enrolment trends, financial viability, Eth