This book was mainly aiming at identifying the effects of medium of instruction (MoI) on curriculum implementation in higher learning institutions. Both qualitative and quantitative approaches were used to collect and analyze data. The results of the study show that the MoI has irreplaceable role in curriculum implementation because it helps to cater for learner centeredness approach, it facilitates also during assessment and evaluation, in teaching and learning activities and consultation of material resources, since it is well mastered. However, the findings show that being passive in learning, lack of information from teaching and learning references and giving improper answers during assessment and evaluation are among challenges met by some lecturers and students related to MoI proficiency and MoI change that took place in Rwanda since 2008. To handle some of those problems, especially in classroom setting, code mixing and code switching intervene depending on a given circumstance; which could not be applied in normal teaching and learning process.