Thaqalain tradition is a famous and well-known tradition that is reported by [both] Sunnites and Shiites. Hundreds of prominent narrators have narrated this tradition. Some self-interested figures have fabricated the tradition of adherence to Book (Quran) and Tradition (Prophet's Tradition) [instead of Quran and Prophet's Progeny] as two weighty things. This book studies this tradition and its reporters, critically examines them and shows the truth to those who seek it.