This chapter traces the development of the theory of lay epistemics as it has unfolded over the last three decades. The chapter describes the serendipitous beginnings of the theory, its roots in twentieth-century philosophy and sociology of science, and its reaction to social cognitive theory on attribution and consistency processes. The general theoretical depiction of the knowledge formation process gave rise to three streams of lay epistemic research described herein. The respective research programs revolve around (1) the evidential base of knowledge formation giving rise to research on the unimodel, (2) the unique sociopsychological nature of evidence giving rise to research on epistemic authority, and (3) the motivational basis of knowledge formation giving rise to research on the need ...