Psychologist: These folks are considered to be at the top of the ladder of non-medical counseling providers. In most states, a newly licensed professional must have attained a Ph.D. (doctorate) from the psychology department of an accredited college and have passed a national licensing exam. Usually, they have spent at least two years in supervised practice before they are eligible to take their exam. Once they are licensed, in most states, they are allowed to supervise other counseling providers not yet licensed.
Psychiatrist: These folks are medical doctors (MD) who, in their final years of medical school, internships or residencies, specialized in the treatment of mental disorders. Most psychiatrists operate in the medical model, focusing on brain chemistry, and prescribe medication as a means of alleviating symptoms. They often work with or supervise mental health professionals who will actually provide the counseling in conjunction with the prescribed medication. Some psychiatrists actually do the counseling themselves. Historically, these medical doctors were the first modern professional counselors (i.e. Freud, Jung, Adler, Rogers, etc.)
Counselor: While this title may seem redundant, it's actually another "branch" of counseling professionals. All counselors must have a Master's Degree in an approved curriculum of Counseling Education, a minimum of 2 years individual counseling, and a passing score on a State or National License Exam to practice. There are two levels of counselors (given different titles depending on the state). The first level requires supervision from another licensed professional, while the second level can practice independently and diagnosis and treat mental and emotional disorders as described in the DSM IV.
Social Worker: Licensed Independent Social Workers (LISW) usually hold at least a Masters Degree (MSW or MA) in social work, and have at least one year of supervised practice before they are allowed to sit for their exam. Social workers often work in agencies, where they do many other kinds of work besides (or instead of) counseling.
Certified Chemical Dependency Counselor: The actual title will vary from state to state. Some states may not even have this certification. Essentially, the folks with the most advanced certification in this field are able to practice independently, to run recovery programs for drug, alcohol, and other addictions, and to supervise other workers in their program. Most folks who are actually independently practicing also are operating as licensed counselors, social workers, or psychologists.
Minister/priest: Because of separation of church and state, no state government can determine the qualifications or education necessary for a person to become ordained in their church, as a result, the kind and the amount of training varies tremendously. In spite of this, many church goers feel most comfortable working with their pastor on personal problems.
Other certifications/licenses: Music, Movement, and Art therapy are slowly becoming state certified professions. Practitioners are usually trained in schools of psychology or social work, and, therefore, have education's comparable to licensed practitioners in those fields, but specialize in offering therapeutic work through the above disciplines. Some practitioners don't fit into the licensed areas either because of alternative methods of education or because they didn't choose to pursue a license. This would also be true for fields such as aroma therapy or herbal therapy. Hypno-therapy works the same way. Most practitioners are actually licensed in psychology, social work, or counseling, but others are only certified by hypno-therapy associations because they either don't have the education or choose for personal reasons not to pursue standard licenses.