Engineering is the discipline and profession of applying scientific knowledge and utilizing natural laws and physical resources in order to design and implement materials, structures, machines, devices, systems, and processes that realize a desired objective and meet specified criteria.

The American Engineers' Council for Professional Development, also known as ECPD, (later ABET), defines Engineering as: the creative application of scientific principles to design or develop structures, machines, apparatus, or manufacturing processes, or works utilizing them singly or in combination; or to construct or operate the same with full cognizance of their design; or to forecast their behavior under specific operating conditions; all as respects an intended function, economics of operation and safety to life and property

Main branches of engineering:
- Aerospace Engineering - The design of aircraft, spacecraft and related topics.
- Chemical Engineering - The conversion of raw materials into usable commodities.
- Civil Engineering - The design and construction of public and private works, such as infrastructure, bridges and buildings.
- Electrical Engineering - The design of electrical systems, such as transformers, as well as electronic goods.
- Mechanical Engineering - The design of physical or mechanical systems, such as engines, power trains, kinematic chains and vibration isolation equipment.

Engineers apply the sciences of physics and mathematics to find suitable solutions to problems or to make improvements to the status quo. If multiple options exist, engineers weigh different design choices on their merits and choose the solution that best matches the requirements. The crucial and unique task of the engineer is to identify, understand, and interpret the constraints on a design in order to produce a successful result. It is usually not enough to build a technically successful product; it must also meet further requirements. Constraints may include available resources, physical, imaginative or technical limitations, flexibility for future modifications and additions, and other factors, such as requirements for cost, safety, marketability, productibility, and serviceability. By understanding the constraints, engineers derive specifications for the limits within which a viable object or system may be produced and operated.

Engineering is a subject that ranges from large collaborations to small individual projects. Almost all engineering projects are beholden to some sort of financing agency: a company, a set of investors, or a government. The few types of engineering that are minimally constrained by such issues are pro bono engineering and open design engineering. By its very nature engineering is bound up with society and human behavior. Every product or construction used by modern society will have been influenced by engineering design. Engineering design is a very powerful tool to make changes to environment, society and economies, and its application brings with it a great responsibility, as represented by many of the Engineering Institutions codes of practice and ethics. Whereas medical ethics is a well-established field with considerable consensus, engineering ethics is far less developed, and engineering projects can be subject to considerable controversy. Just a few examples of this from different engineering disciplines are the development of nuclear weapons, the Three Gorges Dam, the design and use of Sports Utility Vehicles and the extraction of oil. There is a growing trend amongst western engineering companies to enact serious Corporate and Social Responsibility policies, but many companies do not have these.

Engineering is a well respected profession. For example, in Canada it ranks as one of the public's most trusted professions. Sometimes engineering has been seen as a somewhat dry, uninteresting field in popular culture, and has also been thought to be the domain of nerds. For example, the cartoon character Dilbert is an engineer. One difficulty in increasing public awareness of the profession is that average people, in the typical run of ordinary life, do not ever have any personal dealings with engineers, even though they benefit from their work every day. By contrast, it is common to visit a doctor at least once a year, the chartered accountant at tax time, and, occasionally, even a lawyer. In science fiction engineers are often portrayed as highly knowledgeable and respectable individuals who understand the overwhelming future technologies often portrayed in the genre. The Star Trek characters Montgomery Scott, Geordi La Forge, Miles O'Brien, B'Elanna Torres, and Charles Tucker are famous examples.

Scientists study the world as it is; engineers create the world that has never been.
-Theodore von Kármán


Something that people don’t always understand is that engineering is not a spreadsheet full of numbers and equations. It can be Science, Medicine and Biology, Art and a variety of other fields. There are even Social engineering and Political engineering, which deal with forming political and social structures using engineering methodology coupled with political science principles.