Epistemological belief system and its effects on learning have drawn attention of educational researchers in recent years. The article reviewed the philosophical origin of the debate of the different epistemological belief systems and appraised the current research on epistemological beliefs. It is concluded that, after centuries of debate among philosophers and psychologists, a consensus of constructivism has been reached that knowledge is constructed by learners in social contexts. The article also discussed the potential of changing people's epistemological beliefs as means to enhance learning.