Branches of Science: A Complete Guide to Scientific Disciplines and Research Fields

Science is not one activity but a family of them, organized over centuries into a small number of major groupings and a much larger, still-growing set of individual disciplines. This guide is CASRAI’s anchor index for that whole landscape: how the major branches relate to each other, what each one actually studies, and which sub-disciplines sit underneath it. Where a discipline has its own dedicated deep-dive on this site, it’s linked directly. This index is deliberately built to grow — new discipline-level guides are added to it on an ongoing basis, so treat the linked list below as a living library rather than a closed set.

How science is organized: the four major groupings

Almost every individual scientific discipline falls into one of four broad categories, distinguished by what kind of question they ask and what kind of evidence answers it.

Grouping	What it studies	How claims are tested	Examples
Natural sciences	The physical and living world	Observation and experiment	Physics, chemistry, biology, astronomy, geology
Formal sciences	Abstract systems and formal structures	Logical proof and internal consistency, not empirical data	Mathematics, logic, computer science, statistics
Social sciences	Human behavior, society, and institutions	Observation, survey, and experiment applied to people and groups	Psychology, sociology, economics, political science, anthropology, linguistics
Applied sciences & engineering	Solving practical problems using knowledge from the other three groupings	Whether the solution works, in addition to whether the underlying theory is sound	Medicine, engineering, agricultural science

The sections below work through each grouping in turn. Within each one, look for the discipline names in bold — those are the individual fields, and where CASRAI has published a dedicated guide to one, it’s linked directly so you can go deeper.

Natural sciences

The natural sciences study the physical universe and the living things in it, through observation and experiment. They split into two large halves: the physical sciences (matter, energy, and the non-living universe) and the life sciences (living organisms).

Physical sciences

The physical sciences study matter, energy, and their interactions at every scale, from subatomic particles to the observable universe.

• Physics — the study of matter, energy, motion, and force. Its major branches include classical mechanics, thermodynamics, electromagnetism, quantum mechanics, particle physics, condensed matter physics, and astrophysics, the branch of physics applied to stars, galaxies, and the universe as a whole.
• Chemistry — the study of the composition, structure, properties, and reactions of matter. Its major branches include organic chemistry (carbon-based compounds), inorganic chemistry (everything else), physical chemistry (the physics underlying chemical systems), analytical chemistry (identifying and measuring substances), and biochemistry, which sits at the boundary with the life sciences by studying the chemical processes inside living organisms.
• Astronomy — the observational study of celestial objects, distinguished from astrophysics by its focus on cataloguing and observing rather than modeling the underlying physics; the two fields overlap heavily and are often practiced together. See what is astrophysics for the physics-driven branch in detail.
• Earth sciences (geosciences) — the study of the Earth itself, comprising geology (rock, mineral, and structural history), meteorology (atmosphere and weather), climatology (long-term climate systems), oceanography (the oceans), and seismology (earthquakes and the Earth’s interior).

Life sciences: the branches of biology

Biology is the study of living organisms — their structure, function, growth, origin, evolution, and distribution. It is the broadest of the natural sciences by number of sub-disciplines, and several of its branches are substantial fields in their own right:

• Genetics — how traits are inherited and how genes function, mutate, and are expressed.
• Molecular biology — biological activity at the level of DNA, RNA, and proteins.
• Ecology — how organisms interact with each other and their environment.
• Neuroscience — the structure and function of the nervous system, from single neurons to cognition and behavior.
• Immunology — how organisms defend themselves against pathogens and foreign substances.
• Virology — the biology of viruses: their structure, replication, evolution, and the diseases they cause.
• Epidemiology — the distribution and determinants of disease across populations, and the population-level branch of biology and public health most directly tied to human health outcomes.
• Botany — the biology of plants, including their structure, growth, and classification.
• Zoology — the biology of animals, including physiology, behavior, and classification.
• Microbiology — organisms too small to see without a microscope: bacteria, fungi, protists, and archaea (virology is often treated as a microbiology sub-branch, though viruses are not classified as living organisms in the same sense).
• Physiology — how the parts of an organism — organs, tissues, cells — function and work together.

Biology’s branches are frequently combined into hybrid fields — biochemistry (chemistry + biology), biostatistics (statistics + biology), and biophysics (physics + biology) are the three most established examples, and each is covered as its own discipline elsewhere on this page or in its own linked guide.

Formal sciences

The formal sciences study abstract systems, and their claims are established through logical proof or internal consistency rather than through observing the physical world. They underpin the methods used across every other grouping.

• Mathematics — the study of quantity, structure, space, and change, spanning branches like algebra, geometry, calculus, and number theory.
• Computer science — the theory of computation, algorithms, and information, plus the practical engineering of software and systems.
• Logic — the formal study of valid reasoning and argument structure.
• Statistics — the collection, analysis, interpretation, and presentation of data, and the mathematical basis for drawing sound conclusions from it. Biostatistics is the branch applied specifically to biological, medical, and public-health data.

Social sciences

The social sciences study human behavior, relationships, and institutions, using observational, survey, and experimental methods adapted to people and social systems.

• Psychology — individual mind and behavior.
• Sociology — societies, social relationships, and institutions.
• Economics — the production, distribution, and consumption of goods and services, and how individuals and institutions allocate scarce resources.
• Political science — political systems, governance, and power.
• Anthropology — human societies and cultures, including their biological and archaeological history.
• Linguistics — the structure, use, and evolution of human language.

Applied sciences & engineering

Applied sciences take findings from the natural, formal, and social sciences and use them to solve practical problems. This grouping is where most professional scientific and technical careers sit.

• Medicine and health sciences — the diagnosis, treatment, and prevention of disease. This is one of the largest applied groupings and includes its own dense set of sub-disciplines: pharmacology (how drugs affect the body), toxicology (the effects of harmful substances), and — overlapping with the life sciences above — immunology and epidemiology. Clinical and hospital-side research and administration around this work is covered in depth in CASRAI’s clinical research administration and patient safety & infection prevention hubs.
• Engineering — the design and construction of systems, structures, and machines, applying physics, chemistry, and mathematics to practical ends. Major branches include mechanical, electrical, civil, chemical, and biomedical engineering, plus computer engineering (the hardware-focused counterpart to computer science).
• Agricultural science — food and fiber production, applying biology, chemistry, and ecology to crops, soil, and livestock.

For the software, instrumentation, and lab-management side of doing this work day to day, see CASRAI’s research tools & software and laboratory operations hubs.

Types of scientists: who works in each branch

Every discipline above has a corresponding practitioner title. This is not an exhaustive list of every possible job title in science, but it covers the practitioner name for each major branch and sub-branch discussed above.

Branch	Practitioner is called a…
Physics	Physicist
Chemistry	Chemist
Astronomy / Astrophysics	Astronomer / Astrophysicist
Geology	Geologist
Meteorology	Meteorologist
Oceanography	Oceanographer
Biology (general)	Biologist
Genetics	Geneticist
Ecology	Ecologist
Neuroscience	Neuroscientist
Immunology	Immunologist
Virology	Virologist
Epidemiology	Epidemiologist
Microbiology	Microbiologist
Botany	Botanist
Zoology	Zoologist
Mathematics	Mathematician
Computer science	Computer scientist
Statistics / Biostatistics	Statistician / Biostatistician
Psychology	Psychologist
Sociology	Sociologist
Economics	Economist
Anthropology	Anthropologist
Linguistics	Linguist
Medicine / Pharmacology / Toxicology	Physician / Pharmacologist / Toxicologist
Engineering	Engineer (qualified by branch, e.g. mechanical engineer)
Agricultural science	Agricultural scientist / Agronomist

STEM fields list: what counts as STEM

STEM is not a fifth category alongside the four groupings above — it’s a cross-cutting label covering Science, Technology, Engineering, and Mathematics fields collectively, as distinct from the humanities and arts. In practice, a STEM fields list draws from across the groupings on this page:

• Science — the natural sciences (physics, chemistry, biology, earth sciences, astronomy) and, in most STEM classifications, the formal sciences (mathematics, statistics, computer science) and health sciences as well.
• Technology — applied computing and information technology fields, closely tied to computer science.
• Engineering — every engineering branch listed above.
• Mathematics — mathematics and statistics.

Social sciences (psychology, sociology, economics, political science, anthropology, linguistics) are sometimes included in broader STEM definitions and sometimes excluded, depending on the classification system in use (this varies, for example, between different national funding-agency and workforce-statistics definitions) — there is no single universally-binding STEM boundary, which is why STEM fields lists vary somewhat from source to source.

The complete list of scientific disciplines: explore each field in depth

This page is the index; the individual discipline guides are where the real depth lives. CASRAI is actively building out dedicated, in-depth guides to individual scientific disciplines — the list below is what’s live today, and it will keep growing. Bookmark this page rather than a static list: new disciplines are added on an ongoing basis.

• What Is Ecology? — organisms and their environment
• What Is Epidemiology? — disease patterns across populations
• What Is Genetics? — heredity and gene function
• What Is Neuroscience? — the nervous system and brain
• What Is Astrophysics? — the physics of stars, galaxies, and the universe
• What Is Biochemistry? — the chemistry of living systems
• What Is Pharmacology? — how drugs affect the body
• What Is Toxicology? — the effects of harmful substances
• What Is Immunology? — the immune system and defense against disease
• What Is Molecular Biology? — biology at the level of DNA, RNA, and proteins
• What Is Biostatistics? — statistics applied to biological and health data
• What Is Virology? — the biology of viruses

For the broader research-methods context these disciplines all sit inside — study design, sampling, quantitative and qualitative analysis, and measurement — see CASRAI’s research methods & statistics hub.

Frequently asked questions

What are the main branches of biology?

The core branches of biology are genetics, molecular biology, ecology, microbiology, botany, zoology, and physiology, with neuroscience, immunology, virology, and epidemiology as major applied and specialized branches. Hybrid fields like biochemistry and biostatistics combine biology with chemistry and statistics respectively. See the life sciences section above for what each one studies.

What are the branches of chemistry?

The four traditional branches of chemistry are organic chemistry (carbon-based compounds), inorganic chemistry (non-carbon-based compounds and materials), physical chemistry (the physical principles underlying chemical behavior), and analytical chemistry (identifying and quantifying substances). Biochemistry — the chemistry of living systems — is the major branch that bridges chemistry and biology.

What are the branches of physics?

Major branches of physics include classical mechanics, thermodynamics, electromagnetism, quantum mechanics, particle physics, and condensed matter physics, plus applied branches like astrophysics (physics applied to the universe), biophysics (physics applied to living systems), and geophysics (physics applied to the Earth).

What are the different types of scientists?

A scientist’s title generally follows their discipline: physicists study physics, chemists study chemistry, biologists study biology, geologists study geology, and so on down to more specific sub-disciplines — a virologist studies viruses, an epidemiologist studies disease patterns in populations, a biostatistician applies statistics to biological data. See the types-of-scientists table above for a fuller mapping from branch to practitioner title.

Is there a complete list of scientific disciplines?

Not a single official one — the boundaries between disciplines, and how finely they’re split, vary somewhat by classification system (academic department structures, funding-agency taxonomies, and standards bodies each draw the lines slightly differently). What’s stable across virtually all of them is the four-way grouping into natural, formal, social, and applied sciences used throughout this guide, and the identity of the major disciplines within each. This page functions as CASRAI’s working list and will keep expanding as more discipline-level guides are published.

What fields count as STEM?

STEM covers science, technology, engineering, and mathematics fields collectively. The natural sciences, formal sciences, and all engineering branches are consistently included; whether the social sciences count varies by classification system. See the STEM fields section above for the detail.

Why does this page keep changing?

Because it’s designed to. This is CASRAI’s anchor hub for an ongoing series of individual discipline deep-dives — it reflects the disciplines that are live today and is updated as new ones are published, rather than trying to be a single finished, static list.