One of the most common types of certification in modern society is professional certification, where a person is certified as being able to competently complete a job or task, usually by the passing of an examination and/or the completion of a program of study. Some professional certifications also require that one obtain work experience in a related field before the certification can be awarded. Some professional certifications are valid for a lifetime upon completing all certification requirements. Others expire after a certain period of time and have to be maintained with further education and/or testing.