A biologist is a professional who has specialized knowledge in the field of biology, understanding the underlying mechanisms that govern the functioning of biological systems within fields such as health, technology and the environment. Biologists involved in fundamental research attempt to explore and further explain the underlying mechanisms that govern the functioning of living matter. Biologists involved in applied research attempt to develop or improve more specific processes and understanding, in fields such as medicine and industry. Biologists are interested in understanding the underlying mechanisms that govern the functioning of living matter as well as the complex properties that emerge from the biophysical, biochemical, cellular and systemic interactions of living systems. Biologists conduct research using the scientific method to test the validity of a theory in a rational, unbiased and reproducible manner. This consists of hypothesis formation, experimentation and data analysis to establish the validity or invalidity of a scientific theory. There are different types of biologists. Theoretical biologists use mathematical methods and develop models to understand phenomena and ideally predict future experimental results, while experimental biologists conceive experiments to test those predictions. Some biologists work on microorganisms, while others study multicellular organisms (including humans). Some investigate the nano or micro-scale, others emergent properties such as ecological interactions or cognition. There is much overlap between different fields of biology (e.g. zoology, microbiology, genetics and evolutionary biology) and due to the interdisciplinary nature of the field it is often difficult to classify a life scientist as only one of them. Many biological scientists work in research and development. Some conduct fundamental research to advance human knowledge of life. Furthermore, applied biological research often aids the development of solutions to problems in areas such as human health and the natural environment. Biological scientists mostly work in government, university, and private industry laboratories.