The engineering industry comprises many fields of study, all employing unique and sometimes similar methods of science to reach practical solutions to problems and questions in all industries. There are five basic areas of study in which engineers in all branches of the industry can specialize: research, development, application, management, and maintenance. While an engineer may work exclusively in one of these areas, it is more common for their knowledge and duties to overlap. For example, research and development are commonly linked and called R&D. Those working in the application side of a project may often find themselves making maintenance calls.

All engineering projects begin with research. The type and scope of research will be different in each branch of engineering, but generally, once a goal has been set by an industry or institution and brought to the engineers, they set out to find possible ways to accomplish it. Some research engineers work independently, seeking to find new principles and processes for a specific branch of engineering.

Closely tied to research is development. Development entails applying the results of a research project to a specific function. Since there may be more than one way of doing this, a development team must perform tests and studies to find the best way. A research engineer may have come up with several usable materials for a part on an airplane, but it is up to the development team to figure out which of those materials works best in the big picture.

With the research and development complete, the real fun begins—project application. Engineers use the data from the R&D studies and apply them to the design and production of materials, machines, methods, or to whatever the ultimate goal is. For example, a team of civil engineers, after finding the best materials and location for building a bridge in Alaska, will then set out to design and build the bridge.

A management engineer, who earlier may have been part of the R&D or application team, will be responsible for keeping the developed idea working. Management engineers study their work as it was intended to function—whether it is machinery, a drawbridge, or a carving knife—and look for ways to improve on it in the future. If a team of electrical engineers designs a new system of electronic circuits for a home entertainment system, management engineers may find that, once everything is in place and the system has been manufactured, there are certain minor aspects that can be improved.

Maintenance, the final stage in an engineering project, is concerned with the project's upkeep. A team of mechanical engineers, for example, may have designed a machine to package coffee in tin containers. The engineers visit the plant, set it up, and go home with everyone satisfied. Two months later, a maintenance engineer, who was likely involved in the application process, is called back to the plant to fix a problem. These sorts of maintenance calls are fairly common, as it takes a while with any new project to work out the bugs.

Engineers in a particular industry, say in nuclear engineering, will be trained in nuclear engineering, but they will also have to understand the principles, both basic and complex, of other branches of engineering. Depending on their specific studies, the nuclear engineers may need understanding of environmental, chemical, aerospace, mechanical, electrical, industrial, materials, naval, or computer engineering.

Professional Engineer, or PE, is a special title like Ph.D., which indicates that the engineer has completed education and experience requirements and has passed required exams. There were 1.7 million engineers in the United States in 2018 according to the U.S. Department of Labor. The largest number of engineers work in civil, mechanical, industrial, electrical, and electronics engineering. Among the largest employers of engineers were semiconductor and electronics manufacturers, communication equipment manufacturers, and the aerospace industry.

Engineers are needed in virtually every field, whether for a small company or a large firm, indoors or outdoors, nine to five or the graveyard shift. As a mechanical, automobile, chemical, industrial, plastics, or robotics engineer, employment may be with an automobile manufacturer, as well as at any of the thousands of private manufacturing companies. Civil engineers can find jobs with local and city governments, with construction firms, with the military or federal government, and even large corporations. Petroleum and chemical engineers seek jobs with petroleum and gas companies like Shell, Texaco, and ExxonMobil Corporation, or with major chemical companies like Dow, Eastman Chemical Company, or DuPont. Environmental and biological engineers work at the Environmental Protection Agency, industry, or consulting firms. Companies producing high-tech equipment for commercial and industrial use look for skilled electrical engineers, as well as software, mechanical, materials, and plastics engineers.

Engineers are also employed by local, state, and the federal government. Some federal employers of engineers include the National Aeronautics and Space Administration, and the Departments of Agriculture, Defense, Energy, Interior, and Transportation. Other employment possibilities for engineers are in academia as instructors or researchers, at engineering firms, or as independent consultants.