Industries are usually grouped into three sectors: primary (taking resources from nature: farming, forestry, fishing, mining), secondary (making things: manufacturing and construction) and tertiary (services). The three-sector idea was popularised by economist Colin Clark in The Conditions of Economic Progress (1940), who found that richer countries employ a larger share of workers in services. Teachers often add a quaternary (knowledge) and quinary (top decision-making) sector; official statistics instead use detailed codes such as the UN’s ISIC.
Extracting or growing raw materials. Clark defined primary industries as agriculture, forestry and fishing; he placed mining in the secondary group, while most modern teaching puts it in primary.
02
Secondary
Turning materials into goods: manufacturing, construction and, in most schemes, energy and water supply.
03
Tertiary
Services sold to people and businesses: commerce, transport, finance, health, education, hospitality and government.
04
Quaternary and quinary
Extensions of the tertiary sector used in teaching: knowledge work such as research and IT, and the highest-level decisions in government, business and science. They are not separate categories in official classifications.
Where you see it today
Services are now half of all jobs
World Bank data (modelled ILO estimates, updated October 2026) put services at 50.6% of world employment in 2025, up from 35.4% in 1991. Agriculture fell from 42.8% to 25.8% over the same years, and industry moved from 21.8% to 23.7%. Clark’s pattern has held at world scale.
The classification itself was updated
The UN Statistical Commission endorsed revision 5 of the International Standard Industrial Classification (ISIC) at its 54th session in 2023. It has 22 sections, from agriculture to extraterritorial bodies.
Platforms got their own codes
ISIC Rev.5 adds classes for intermediation service activities, for example for passenger transport, accommodation and food services. As we read it, these fit the platform model of ride-hailing, booking and delivery apps that match buyers and sellers.
Computing infrastructure is named
ISIC Rev.5 groups telecommunications, programming, consultancy and computing infrastructure in one section, with a class for computing infrastructure, data processing and hosting. The data centres behind AI now sit in the industrial map as their own activity.
The five sectors at a glance
Primary
What it doesTakes resources from nature
ExamplesCrop farming, fishing, forestry, mining
Secondary
What it doesMakes goods and builds
ExamplesCar making, chemicals, construction, power generation
ExamplesResearch labs, software, data processing, consulting
Quinary (teaching term)
What it doesTakes top-level decisions
ExamplesSenior government, chief executives, heads of research
How to use it
Use the sector model to explain an economy's shape; use official codes (ISIC, or NAICS in North America) for any data work.
When sizing a market, find the exact ISIC or NAICS class first, so your numbers match official statistics.
Check whether a company sells goods, services or a platform: the same app can sit in different classes.
Track where your customers' jobs are moving; demand follows the shift to services and knowledge work.
For AI businesses, map both sides: the compute and data infrastructure, and the service industries buying it.
The Business Engineer lens
AI does not add a new sector so much as cut across all of them: it needs heavy infrastructure and sells into services. The Business Engineer reads industry lines as starting points, and looks for where AI moves value between them.
Primary (resources from nature), secondary (manufacturing and construction) and tertiary (services). Teachers often add quaternary (knowledge) and quinary (top decision-making).
It is associated with economist Colin Clark, whose 1940 book The Conditions of Economic Progress grouped industries into primary, secondary and tertiary.
Which sector employs the most people?
Services. World Bank modelled ILO estimates put services at 50.6% of world employment in 2025.
How are industries officially classified?
With standard codes such as the UN's ISIC, whose fifth revision was endorsed in 2023 and has 22 sections, or NAICS in North America.
Every organization operates in at least one industry, with some operating in several. An industry can simply be defined as a group of companies with similar business activities, products, and services. There are now five main types of industry: primary, secondary, tertiary, quaternary, and quinary. In this article, weโll discuss the differences between each and list some specific examples.
Industry Type
Description
Examples
Agriculture
Farming, forestry, and fishing activities.
Crop farming, cattle ranching, forestry.
Automotive
Manufacturing and selling automobiles.
Ford, Toyota, General Motors.
Aviation
Airlines, aircraft manufacturing, and services.
Delta Airlines, Boeing, Airbus.
Banking and Finance
Banking, investment, and financial services.
JPMorgan Chase, Goldman Sachs, Visa.
Biotechnology
Research and development in biological sciences.
Genentech, Amgen, CRISPR Therapeutics.
Chemical
Chemical manufacturing and related industries.
Dow Chemical, BASF, DuPont.
Construction
Building and infrastructure construction.
Turner Construction, Bechtel, Skanska.
Education
Schools, colleges, and educational services.
Harvard University, Khan Academy, Pearson.
Energy
Power generation, renewable energy, utilities.
ExxonMobil, Tesla, National Grid.
Entertainment
Film, television, music, and gaming industries.
Disney, Warner Bros., Sony Music, Electronic Arts.
Food and Beverage
Production and distribution of food and drinks.
Coca-Cola, McDonald’s, Nestlรฉ.
Healthcare
Hospitals, clinics, pharmaceuticals, medical devices.
Pfizer, Johnson & Johnson, Mayo Clinic.
Hospitality
Hotels, restaurants, and tourism-related businesses.
Marriott, Hilton, Airbnb, Starbucks.
Information Technology
Software, hardware, and technology services.
Apple, Microsoft, Google, IBM.
Insurance
Insurance companies and related services.
Allstate, AIG, Prudential.
Manufacturing
General manufacturing of various products.
General Electric, 3M, Procter & Gamble.
Media
Newspapers, magazines, online media, and publishing.
The New York Times, CNN, Netflix.
Mining
Extraction of minerals and natural resources.
Rio Tinto, BHP, Freeport-McMoRan.
Real Estate
Property development, sales, and management.
Keller Williams Realty, CBRE, Zillow.
Retail
Sales of goods to consumers through stores or online.
Walmart, Amazon, Target.
Telecommunications
Communication networks and services.
AT&T, Verizon, Ericsson.
Transportation
Shipping, logistics, and transportation services.
FedEx, UPS, Maersk Line, Uber.
Utilities
Water, gas, and electric utilities.
PG&E, E.ON, American Water Works.
Waste Management
Collection and disposal of waste materials.
Waste Management Inc., Republic Services.
Pharmaceutical
Manufacturing and distribution of pharmaceuticals.
Pfizer, Johnson & Johnson, Novartis.
Aerospace
Space exploration, aircraft, and satellite production.
Primary industries are those that extract natural resources such as minerals, soil, plants, water, and those consumed to produce energy.
This includes industries such as:
Mining โ where metals, minerals, oil, gas, coal, and other resources are extracted from the Earthโs surface.
Agriculture โ with a primary focus on cultivating plants, land, and animals to produce food, drink, and other essential items.
Forestry โ companies in the forestry industry manage and log native forest or timber plantations to produce wood for construction and furniture, among other uses.
Fishing โ the fishing industry encompasses any activity associated with the catching, culturing, processing, harvesting, or selling of fish. This includes recreational, commercial, and subsistence fishing.
Hunting โ or the practice of killing native or feral animals to harvest animal products, including meat, bone, fur, antlers, or tusks. The hunting industry also encompasses the act of removing predators dangerous to humans, taxidermy, and trophy hunting.
Secondary industries
Secondary industries add value to the natural resources acquired by primary industries. They do this by converting raw materials into useful and profitable products for consumers and other businesses. For this reason, secondary industry is sometimes called the manufacturing industry.
Secondary industry examples include:
Manufacturing โ where businesses convert raw components and materials into products. This is often done at scale in highly automated factories to produce low unit cost items.
Construction โ a broad industry dealing with the construction of residential, commercial, and industrial buildings. The construction industry also includes road, rail, tunnel, dam, and bridge infrastructure.
Food and beverage โ which involves the processing, preserving, and serving of food items. The food and beverage industry works closely with the agriculture industry to produce fresh and long-life food items for restaurants, supermarkets, and other food retailers.
Fashion โ or the design, production, and marketing of clothing, footwear, and other items that are worn by people.
Technology โ another broad industry category characterized by the innovation, design, and production of computers, software, apps, aerospace equipment, military equipment, and health care technology.
Tertiary industries
In a tertiary industry, the major economic activities include:
Exchange โ or transportation, trade, and communication services that are used to bridge distance.
Production โ or the supply of a diverse range of services utilized by millions of people.
Tertiary industries are mostly commerce and service-related businesses that produce non-tangible value. Examples of tertiary industries, which are a hallmark of wealthy and advanced nations, include:
Professional services โ these are jobs requiring specialized knowledge or training, such as engineers, physicians, lawyers, architects, accountants, surgeons, dentists, and high-level administrators.
Telecommunications โ encompassing the transmission of signals, words, messages, sounds, images, or any other information via infrastructure such as cables, the internet, radio, and television.
Franchise โ where one company, the franchisor, gives the right for another company, the franchisee, to utilize its brand, systems, or other intellectual property. Many franchisors utilize this model to create commercial chains for the distribution of goods and services.
Education โ the education industry includes universities, schools, colleges, or training providers that help consumers acquire knowledge, skills, values, morals, or beliefs.
Entertainment โ an industry with many sub-industries devoted to the singular or mass entertainment of people, including comedy, film, music, theatre, and sport.
Quaternary industries
The definition of a quaternary industry is harder to define, but in general, it is any industry based on new technology and specialized knowledge. These industries are characterized by the individual relying on their education and intelligence to generate and operate advanced technologies.
Since it requires highly advanced technology, the quaternary industry is relatively young. Furthermore, it is only present in modern economies where the generation, analysis, and dissemination of knowledge is important enough to warrant it being separated from tertiary sectors.
Quaternary industries include:
Finance โ including corporate finance, banking, personal finance, investing, and asset management.
Consultancy โ where specialists offer advice to businesses in a range of areas.
Research and development โ or innovative activities undertaken by governments and corporations to develop new products and services or improve existing ones.
Quinary industries
Quinary industries focus on the creation, re-arrangement, and interpretation of new or existing ideas. They also deal with the use and evaluation of new technologies.
Many economists refer to those involved in quinary industries as โgold-collar professionalsโ because they hold extremely desirable skills and are involved in high-level decision-making.
Quinary industries may encompass specific sections of tertiary or quaternary industries, including government, science, education, health care, culture, media, and non-profit organizations.
To a lesser degree, some also suggest the domestic activities performed in a home by a family member or dependent are part of the quinary industry. These activities, which include housekeeping, child care, animal care, and maintenance, are typically unpaid and so are not measured by their monetary value. Nevertheless, they contribute to the economy by providing free services that would otherwise have to be paid for.
Key takeaways:
While businesses may operate in one or more different industries, an industry can simply be defined as a group of companies with similar business activities, products, and services. Industries are categorized into five broad types: primary, secondary, tertiary, quaternary, and quinary.
Primary industries extract raw materials from the Earth, including mining, agriculture, forestry, fishing, and hunting. Secondary industries, which turn those raw materials into useable products, include manufacturing, construction, food and beverage, fashion, and technology.
Tertiary industries include any service that results in the creation of intangible value, such as those seen in professional services, telecommunications, franchising, education, and entertainment. In general, quaternary and quinary industries are associated with highly specialized knowledge and technology that tends to be found in modern, developed nations.
How AI Is Changing This
Artificial intelligence is revolutionizing manufacturing through predictive maintenance systems that fundamentally transform how factories operate. General Electric’s Predix platform exemplifies this transformation by using AI algorithms to analyze data from thousands of sensors embedded in industrial equipment like turbines, compressors, and assembly line machinery. The system continuously monitors vibration patterns, temperature fluctuations, and performance metrics to predict equipment failures weeks or months before they occur. This allows manufacturers to schedule maintenance during planned downtime rather than experiencing costly unexpected breakdowns. At GE’s own facilities, this AI-driven approach has reduced unplanned downtime by up to 20% and maintenance costs by 10-15%. The technology has shifted the entire industry from reactive “fix-when-broken” maintenance to proactive, data-driven operations, enabling manufacturers to optimize production schedules, extend equipment lifespan, and significantly improve overall operational efficiency across their facilities.
Primary Industries: Involve the extraction of natural resources like minerals, plants, water, and energy sources. Examples include mining, agriculture, forestry, fishing, and hunting.
Secondary Industries: Add value to raw materials through manufacturing processes. This category includes manufacturing, construction, food and beverage production, fashion, and technology.
Tertiary Industries: Focus on providing services and often involve commerce and non-tangible value. Examples are professional services (doctors, lawyers), telecommunications, franchise businesses, education, and entertainment.
Quaternary Industries: Rely on advanced technology and specialized knowledge. It includes finance, consultancy, research and development (R&D), and other high-level innovative activities.
Quinary Industries: Deal with the creation, interpretation, and use of new ideas, often involving high-level decision-making. These industries encompass sectors like government, science, education, healthcare, culture, media, and non-profit organizations.
Gennaro Cuofano is a CRO and tech executive who has worked in AI since late 2015, starting with bringing NLP, natural-language generation, voice and chatbot products to the marketing industry. His background is in law and finance: he holds a Master's degree in Law and an International MBA with an emphasis on corporate finance (LUISS Business School and the University of San Diego, 2012), and worked as a financial analyst at a real-estate investment firm in San Diego and as an assistant controller. His work focuses on business model strategy, business engineering and, more broadly, structural analysis: how companies make money, read from their own filings. He created FourWeekMBA and leads research there and at The Business Engineer, his newsletter on AI and business strategy, with over 95,000 subscribers and more than 1,000 published analyses. His writing has also appeared on Entrepreneur (for example, How to Digitize a Family Business in Europe) and HackerNoon. Find him on LinkedIn and Substack. See how we source.
The Business Engineer readThe FRED Test: Industry-by-Industry AnalysisEvery technological revolution has a moment of truthโa point where the early adopters separate from the soon-to-be-obsolete.Read on businessengineer.ai โ
