Apprenticeship is a system for training a new generation of practitioners of a trade or profession with on-the-job training and often some accompanying study (classroom work and reading). Apprenticeships can also enable practitioners to gain a license to practice in a regulated occupation. Most of their training is done while working for an employer who helps the apprentices learn their trade or profession, in exchange for their continued labor for an agreed period after they have achieved measurable competencies. Apprenticeship lengths vary significantly across sectors, professions, roles and cultures. In some cases people who successfully complete an apprenticeship can reach the "journeyman" or professional certification level of competence. In other cases they can be offered a permanent job at the company that provided the placement. Although the formal boundaries and terminology of the apprentice/journeyman/master system often do not extend outside guilds and trade unions, the concept of on-the-job training leading to competence over a period of years is found in any field of skilled labor.