At a minimum, social workers need to obtain a four-year degree in the humanities field. Most colleges offer a Bachelor's of Science in Human Studies. After the degree, a social worker must get licensed, register or become certified before he can work.
Social work splits into three fields---child and family social work, medical and public health social work, and mental health and substance abuse social work. Depending on the field of social work, the degree can be geared toward that field. For example, a person wishing to be a child and family social worker can concentrate on child and family welfare.
Those desiring to work in public health or substance abuse can obtain a master's degree geared towards those particular fields. For those desiring to teach college, a Ph.D. must be obtained.