International Standard Classification of Occupations

The International Standard Classification of Occupations (ISCO) is a system developed by the International Labour Organization (ILO) to classify and organize occupations into a structured hierarchy. It serves to facilitate international communication about occupations by providing a framework for statisticians to make internationally comparable occupational data available.
The ILO describes the purpose of the ISCO as:
According to the ILO, a job is defined as "a set of tasks and duties performed, or meant to be performed, by one person, including for an employer or in self-employment." Occupation refers to the kind of work performed in a job, and the concept of occupation is defined as "a set of jobs whose main tasks and duties are characterized by a high degree of similarity." A person may be associated with an occupation through the main job currently held, a second job, a future job, or a job previously held. Skill, in this context, is the ability to carry out the tasks and duties of a job.
The latest version, ISCO-08, was adopted in 2008 and includes four classification levels: major groups, sub-major groups, minor groups, and unit groups. It is widely used for comparative labor market studies, policy development, and international reporting, including within the European Union, the United Nations, and other global institutions.
The origins of ISCO trace back to the mid-20th century when the need for a global occupational classification system became evident at the First International Conference of Labour Statisticians (ICLS) in 1923. The first complete version, ISCO-58, was adopted in 1957 by the Ninth ICLS and published in 1958, providing a systematic method for grouping occupations to support labor market analysis and facilitate international comparisons. Subsequent revisions, including ISCO-68, ISCO-88, and ISCO-08, refined the classification criteria to reflect changing labor market structures, technological advancements, and evolving job roles. Notably, ISCO-88 marked a major departure from the earlier versions by organizing similar occupations into increasingly larger groups based on skill level and specialization.
ISCO has since been widely adopted by national governments and international organizations to align workforce data with global labor market trends. ISCO has been continuously adapted to ensure its relevance amid shifts in employment patterns, technological progress, and the emergence of new economic sectors. Moreover, its role in international labor statistics enables cross-country comparisons, aiding in policy formulation and economic planning.
The ISCO-08 revision was developed through consultations with national governments, labor organizations, and international experts to ensure relevance and adaptability. Key issues addressed in the ISCO-08 revision included the impact of information and communications technology on the labor market's occupational structure, the need for better representation of health organizations, and the lack of detail in ISCO-88 for clerical and service-related occupations, which are predominantly held by women. Looking ahead, future iterations of ISCO are expected to incorporate new occupational categories reflecting automation, digital transformation, and emerging industries.
The adaptation of ISCO-08 for national use is a critical process to ensure its applicability across diverse labor markets. Countries often modify ISCO-08 to align with national occupational classifications while maintaining international comparability. For instance, the European Union, through the European Skills, Competences, Qualifications and Occupations (ESCO) framework, has built upon ISCO-08 by incorporating more detailed competencies and qualifications for cross-border labor mobility. This adaptation process involves mapping national job structures to ISCO categories, refining classifications to reflect local labor market conditions, and ensuring consistency in data reporting for global labor statistics. Of note, Donald Treiman developed the Standard International Occupational Prestige Scale using the ISCO.
ISCO-08 organizes occupations into a four-level hierarchical system:
The ISCO-08 divides jobs into 10 major groups:
Managers
Professionals
Technicians and associate professionals
Clerical support workers
Service and sales workers
Skilled agricultural, forestry and fishery workers
Craft and related trades workers
Plant and machine operators and assemblers
Elementary occupations
Armed forces occupations
The process of assigning occupational responses to ISCO-08 categories is known as coding, which follows specific guidelines to ensure consistency and accuracy. For precise classification, the following core information is required:
Additional information can enhance coding accuracy, such as:
While details about the industry of employment may be useful, they are generally not sufficient for occupational coding on their own. In cases where subsistence farming or fishing plays a major role in a country’s economy, additional data may be collected to distinguish between market-oriented work and own-consumption production. Notably, formal qualifications or skill levels of workers are not always relevant for occupational classification, as individuals often hold qualifications higher or lower than those required for their job. Relying on such information could introduce biases when analyzing the relationship between occupation and education.
Occupational information is typically collected through national censuses and household surveys using three types of questions:
In establishment surveys and administrative data collection, job descriptions or duty statements may be coded directly into ISCO-08 categories using official classification indexes.
Pre-coded questions offer quick and cost-effective processing but have limitations. They do not always align with real-world job terminology and often lack the detail needed for effective classification. Although they take up significant space on survey forms, they can be improved through careful refinement of response categories, particularly for high-priority groups.
Open-ended responses provide more detailed and accurate data, allowing for the assignment of a 4-digit ISCO-08 code. However, they require significant effort to process, as responses must be manually coded using occupational title indexes. Despite the cost, this method remains the most reliable way to obtain precise statistical and administrative data. Common open-ended questions include:
While these questions can yield useful responses, they may also generate vague answers like "manager", "consultant", or "farm work", which are difficult to code reliably. When such responses occur, they should be coded to the highest supported level rather than forced into arbitrary categories. For example, "teacher" may be coded as "2300: Teaching Professionals Not Further Defined." Similarly, if only "medical doctor" is provided, it may be classified as "2210: Medical Doctors Not Further Defined."
Assigning classification codes to open-ended survey responses is a complex process, requiring analysis of job titles, tasks, industry, and workplacengesas. To ensure accuracy, three key documents are needed: coding instructions, a coding index, and query resolution procedures. The coding index, available in various formats, helps match responses to ISCO-08 codes, as natural job descriptions often differ from formal classification names. While national coding indexes should reflect local language use, the ISCO-08 Index of Occupational Titles provides a valuable starting point.
ISCO-08 classifies skills into two key dimensions:
The ISCO-08 skill levels correspond to the International Standard Classification of Education (ISCED-97) groups as follows:
Skill level is typically assigned at the ISCO Major Group level, except for Major Group 1: Managers and Major Group 0: Armed Forces Occupations, where it is primarily applied at the second hierarchical level (Sub Major Group level). Within each major group, organizing occupations into sub-major, minor, and unit groups is mainly based on skill specialization.
ISCO is one of several major occupational classification systems used worldwide. Other prominent systems include the U.S. Standard Occupational Classification (SOC), the European Skills, Competences, Qualifications and Occupations (ESCO), and national classification systems used in various countries.
ISCO is widely used for categorizing jobs across different sectors and countries. However, it has been subject to various criticisms and limitations. One major criticism is the challenge of cross-national comparability. Studies indicate that occupational titles coded under ISCO-08 often vary significantly between countries, raising concerns about the consistency and reliability of classifications. A study found that only 64% of job titles retained the same ISCO-08 4-digit code across multiple countries, highlighting inconsistencies in occupational classification.
Evolving occupational characteristics have also posed challenges to ISCO, which relies on task similarity, duties, and required skills. Factors such as working conditions (including hours, schedules, and remote work) and the work environment (encompassing safety, health considerations, and workplace interpersonal networks) significantly influence occupational categorization.
Moreover, the ISCO framework, which consists of at least ten major occupational groups, is often difficult to apply in small-scale workforce studies or in reporting partial workforce data. As a result, professionals frequently use modified classification systems tailored to specific contexts, such as distinctions between manual and non-manual labor, white- and blue-collar jobs, office-based and outdoor work, or knowledge-based and physical labor.
The ISCO has been criticized for its broad categorization, which can group together jobs with significant differences in tasks, skills, and working conditions. For instance, the ISCO-88 version was noted to have excessive detail in some areas, such as plant and machinery operators, while providing inadequate detail in others, like service-related occupations and those prevalent in the informal sector. Additionally, there was a wide variation in the size of some sub-major and minor groups.