As knowledge of research philosophy is of paramount importance in different paradigms of human sciences, it is also of great significance in qualitative research methodologies. Understanding the ontological, epistemological, and methodological foundations of qualitative research methods enables researchers to more accurately apply each of these methods for each research topic. Additionally, recognizing these fundamental foundations enables the researcher to take advantage of more appropriate strategies in their research. The issue is of necessity since the qualitative research methods are complicated, difficult, and based on the researcher's skills. A better knowledge of the researcher helps him to go through this complex research path. In this book, the fundamental foundations of the dominant qualitative research methodologies are introduced. Moreover, the relationship between these fundamental foundations and the models for entering the experimental reality of research is also discussed to provide an appropriate understanding of these methodologies for the interested scholars and researchers.