In this rapidly changing information, thinking critically is a vital requirement for individuals. In response to this, Indonesian EFL teachers are given responsibility to assist their students to acquire critical thinking skills while learning English. This is done to give them adequate practice in critical thinking so that they can actively participate in the international community particularly in the global workplace.This book presents results of a study aims to investigate students' critical thinking as demonstrated in their argumentative essays. Argumentative writing has been believed as an effective means to portray students' critical thinking. It assists students in making ideas of their own, clarifying opinions or beliefs and sorting out the evidence which are part of critical thinking realization. In addition, this book also provides explanation regarding students' consciousness on their own critical thinking. In this sense, information regarding their awareness as to whether they show critical thinking and individual voice in their argumentative texts has been the object of this book to discuss.