Students wishing to pursue a doctoral program are expected to have a particular level of mastery in the field. Towards this end, universities specify a basic degree in the relevant field as a prerequisite for admission. The degree you need to gain entrance to such programs will vary depending on the field of study as well as the particular university, although almost all programs require a four-year bachelor's degree. It is usually required that your undergraduate degree is in the same field or a closely related one.
In areas where a master's degree better prepares a student for further research work, programs will specify this as the basic criterion, as seen for example in Ph.D. programs in Criminal Justice.
All doctoral programs require scores from at least one of the standardized tests, commonly the Graduate Record Examination (GRE). Some programs, such as Psychology, will require the corresponding GRE Subject Test that measures knowledge in a specific discipline. Some specialized fields will require other exams that demonstrate a candidate's suitability for further study; for example, medical schools require the Medical College Admission Test (MCAT), law schools ask for Law School Admission Test (LSAT) and business schools require the Graduate Management Admission Test (GMAT). Considering the fact that there are more applicants than slots available at graduate schools, many programs specify minimum cutoff scores.
As English is the medium of instruction in all doctoral programs in the U.S., all universities require candidates to possess English language skills. Applicants whose first language is not English should take the Test of English as a Foreign Language (TOEFL). In some cases, graduate schools may also accept scores obtained on the International English Language Testing System (IELTS) test. Just as with the standardized tests, universities sometimes specify cutoff scores for these language tests.
All doctoral programs require letters of recommendations to accompany applications. Letters from faculty in your chosen field of study will carry greater weight than those from faculty in other disciplines. While selecting faculty to approach for these references, it is important to consider their seniority, experience in the field and reputation in academic circles. It is a good idea to provide them with a copy of your resume to help them understand your qualifications and career goals. The resume should provide details of the courses you have taken and any other teaching or research experience you possess.
At the time of applying to the doctoral program, you will have to produce official transcripts of the previous courses you have attended. Besides, colleges also require you to submit a statement of intent, also called a personal statement. It is imperative you write this statement in a manner that convinces the admissions committee of your suitability for the program. Another document you will have to attach is the curriculum vitae (or c.v.), an academic resume that provides information about your qualifications, skills and details of previous teaching and research experience. Some schools will also require you to submit a sample of your writing from your previous degree program.