Guba, Egon, & Lincoln, Yvonna. (2005). In N. Denzin & Y. Lincoln (Eds.), The Sage Handbook of Qualitative Research (3rd Ed.) (pp. 191-215). Thousand Oaks, London, and New Delhi: Sage.
They identify five contemporary qualitative research paradigms: positivism, postpositivism, critical theories, constructivism, and participatory.
Concerning reflexivity, they define it as "the process of reflecting critically on the self as researcher, the 'human as instrument'" (p. 210). They call attention to two ways of interactions here: how research processes are influenced by a researcher's own life and assumptions and how we researchers become ourselves, in other words, how research itself influence researchers.
In the fifth paradigm, participatory one, they added in this article, reflexivity matters. It relies on critical subjectivity and self-awareness, whereas reflexivity may be considered a problem in positivism.