Dear Rajni, IELTS is a Language proficiency exam taken by non native English speaking students to check their English skills before entering a Native English speaking country for higher studies or employment, etc. GRE is an exam written by students who are looking for admission to Graduate, Master and Doctoral programmes. If you are planning on going abroad for Ph.D, GRE helps you than IELTS. GRE has 2 formats in it namely GRE General Test and GRE Subject test. For more information on GRE, please visit our page at: https://studyabroad.careers360.com/articles/what-gre