Chemical engineering is one of the broadest fields of engineering. This stems from the fact that the discipline of chemical engineering is founded on and incorporates all of the basic sciences such as chemistry, physics, mathematics and biology.
The "disciplinary definition" would be that chemical engineering is the profession in which knowledge of mathematics, physics, chemistry and biology, gained by study, experience and practice, is applied with judgement to develop economic and safe ways of converting raw materials or chemicals into more useful products to benefit mankind. 
The "occupational definition" would be that chemical engineering is a field that deals with industrial and natural processes that involve the chemical, physical or biological transformation of matter or energy into forms useful for mankind, economically and safely without compromising the natural environment.
Perhaps, the simplest definition is that chemical engineering is the design, development and management of a wide and varied spectrum of industrial and other endeavors.
The industrial revolution of the early 1800's gave birth to many large-scale chemical plants including the Lead-Chamber method for producing sulfuric acid. The raw materials included a nitrate which, in the final stage of the process, was lost to the atmosphere as nitric oxide gas and had to be replaced by costly fresh nitrate imported from Chile. In 1827, the French chemist Joseph-Louis Gay-Lussac developed a tower that recovered most of the nitrogen oxide gases formed and reduced the consumption of nitrate. The first Gay-Lussac tower was installed at a plant in France in 1837. However, its use was not widespread until a British chemist, John Glover, invented an improved version of the tower, patented in England in 1859. By the 1870s, the Glover–Gay-Lussac system was used throughout Britain and Europe. Because Glover's tower was essentially a mass transfer]tower, he is often considered to be the first chemical engineer.
In 1791, a French physician, Nicholas Le Blanc, patented a method of producing sodium carbonate from sea salt. By 1810, it was in widespread use. However, it produced the hazardous byproducts hydrochloric acid, nitrogen oxides and chlorine gas. In 1811, Augustine Jean Fresnel, a French physicist, discovered a cleaner process for producing sodium carbonate by bubbling carbon dioxide through an ammonia-containing brine. Attempts to build large-scale plants using Fresnel's process were unsuccessful. In 1863, some fifty years later, a Belgian chemist, Ernest Solvay, successfully applied Fresnel's process using a tall gas absorption tower in which carbon dioxide bubbled up through a descending flow of brine, together with efficient recovery and recycling of the ammonia. Use of the Solvay process soon became widespread and it is still used today. Ernest Solvay's work is sometimes thought of as one of the first accomplishments of chemical engineering.
The Haber process for the production of ammonia by combining hydrogen and nitrogen was first patented by a Geraman chemist, Fritz Haber, in 1908. In 1910, an engineer, Carl Bosch, while working for the German chemical company BASF, successfully commercialized the process and secured further patents. It was first used on an industrial scale by the Germans during World War I. Haber and Bosch were later awarded Nobel prizes, in 1918 and 1931 respectively, for their work in overcoming the chemical and engineering problems posed by the use of large-scale high-pressure technology. Their process is often referred to as the Haber-Bosch process and is considered to be one of the major chemical engineering achievements because it made possible the large-scale production of ammonia-based fertilizers that transformed the world's food production. 
Under the British Alkali Act of 1863, an Alkali Inspector and four subinspectors were appointed to curb the discharge into the air of hydrochloric gas from the Le Blanc sodium carbonate plants. During his long career, one of the Alkali Inspectors, George Davis, inspected many of the Lead Chamber, Le Blanc and Solvay plants in the Midland area of England. What he learned convinced him of the necessity for a new branch of engineering that combined applied chemistry and traditional engineering. In 1880, George Davis proposed the formation of a Society of Chemical Engineers which failed to become a reality. In 1887, he gave a series of 12 lectures on industrial chemical operations at the Manchester Technical School. His lectures can be regarded as the forerunner of the discipline of chemical engineering.  In 1901, Davis published a "Handbook of Chemical Engineering". He is considered to be the father of modern chemical engineering.
In 1888, the first chemical engineering curriculum, designed by Lewis Norton, began at the Massachusetts Institute of Technology (MIT). In 1892 and 1894, respectively, the University of Pennsylvania and Tulane University]] in Louisiana also began chemical engineering programs.
In 1908, the American Institute of Chemical Engineers (AIChE) was formed and, in 1922, the Institution of Chemical Engineers (IChemE) was founded in England.
In 1923, MIT Professors William H. Walker, Warren K. Lewis and William H. McAdams produced the classic book "Principals of Chemical Engineering" which greatly stimulated the evolution of chemical engineering in the United States and encouraged the creation of chemical engineering departments in universities worldwide. In that same year, Professor E.C. Williams established the first chemical engineering program in England at the University College London (UCL). 
The process design, operation and management of large-scale industrial facilities such as:
- Petroleum refining processes producing LPG, gasoline, diesel oil, fuel oils, asphalt, lubricants, waxes, etc.
- Natural gas plants that process raw natural gas to become suitable for consumer use by removing impurities and by-product natural gas liquids (NGL).
- Petrochemical and chemical plants producing plastics, synthetic fibers, elastomers, agricultural chemicals (fertilizers, insecticides, herbicides), detergents (soap, shampoo, cleaning solutions), fragrances, explosives, widely used industrial chemicals (such as sulfuric acid, ammonia) and many others.
- Pulp and paper mills producing paper products.
- Fossil fuel power plants fueled by natural gas, fuel oil or coal.
- Nuclear power plants
Designing processes and facilities for:
- Industrial plants that produce all types of paints and coatings.
- Food and drink processing plants that process foodstuffs and drinks of all kinds.
- Pharmaceutical facilities for producing new drugs.
- Biochemical and bioengineering facilities involving fermentation, enzyme technology, and biological waste treatment.
- The production of all manner of adhesives and composite materials for automobiles as well as the aerospace industries.
- Industrial plants producing glass and ceramics.
Environmental engineering tasks such as:
- The design of air pollution and water pollution control and mitigation facilities.
- Performing environmental impact studies and air pollution dispersion modeling studies.
- The selection or design of facilities to comply with governmental environmental protection regulations.
Safety engineering work such as:
- Performing hazardous operation studies (Hazops) and risk analyses
- Establishing and implementing safe operating procedures for industrial facilities.
Research and development in the fields of:
- Fuel cells
- Computer chips
- Other leading edge technologies
In all of the above fields of endeavor, chemical engineers may also function as consultants, lawyers reviewing new technology patents, sales engineers, instrumentation and control engineers, and equipment manufacturers.
In recent years, chemical engineering has become more and more involved in biomolecular engineering. At a 1992 meeting of the National Institutes of Health (NIH), they defined the term, "Biomolecular Engineering," as Research and development at the interface of chemical engineering and biology with an emphasis at the molecular level.
Many universities now offer degree programs in "Chemical and Biomolecular Engineering".    In the future, chemical engineering will not only encompass design work at large scales (e.g., petroleum refineries and petrochemical plants) but will also encompass work at very small scales down to the molecular level.
- Argentina: Asociación Argentina de Ingenieros Químicos (AAIQ)
- Australia: The Chemical College of Engineers Australia
- Brazil: Associação Brasileira de Engenharia Química (ABEQ)
- Canada: Canadian Society for Chemical Engineering (CSChE)
- China: Chemical Industry and Engineering Society of China (CIESC)
- Europe: European Federation of Chemical Engineering (EFCE)
- Germany: Society for Chemical Engineering and Biotechnology (DECHEMA)
- India: Indian Institute of Chemical Engineers (IIChE)
- Japan: Society of Chemical Engineers, Japan (SCEJ)
- Korea: Korea Institute of Chemical Engineers (KIChE)
- Mexico: Instituto Mexicano de Ingenieros Químicos (IMIQ)
- Puerto Rico: Instituto de Ingenieros Químicos de PR (IIQPR)
- South Africa: South African Institution of Chemical Engineers (SAIChE)
- United Kingdom: Institution of Chemical Engineers (IChemE)
- United States: American Institute of Chemical Engineers (AIChE)
- ^ Article III of the Constitution of the American Institute of Chemical Engineers
- ^ Definition of Chemical Engineering From the website of the Department of Chemical Engineering, Worcester Polytechnic Institute
- ^ Same as Reference 2.
- ^ What is Chemical Engineering? From a website sponsored by the Institution of Chemical Engineering (IChemE)
- ^ Chemistry Chronicles by David Kiefer
- ^ Thomas Spencer Baynes, The Encylopaedia Britannica: A Dictionary of Arts, Science and General Literature, Ninth Edition (Volume XXII), Henry G. Allen and Company.
- ^ What is Chemical Engineering? An example of early Chemical Engineering From the website of Cambridge University in England.
- ^ Vacliv Smil (2004), Enriching the Earth: Fritz Haber, Carl Bosch and the Transformation of World Food Production, MIT Press, ISBN 0-262-69313-5.
- ^ The Effect of the Haber Process on Fertilizers
- ^ Setting the Stage for a New Profession, Chemical Engineering in 1888
- ^ Highlights of Chemical Engineering History From the website of the Department of Chemical Engineering, University of Massachusetts Amherst
- ^ George Edward Davis(1901), A Handbook of Chemical Engineering, Davis Brothers.
- ^ Same as Reference 12.
- ^ W.H. Walker, W.K. Lewis and W.H. McAdams (1923), Principles of Chemical Engineering, 1st Edition, McGraw-Hill.
- ^ A History by Peter Rowe and Tony Burgess From the website of the University College London.
- ^ Increasing Involvement in Biotechnology/Pharmaceuticals Editorial in Chemical Engineering Progress (CEP) published by the AIChE, March 2002.
- ^ Same as Reference 16
- ^ Chemical and Biomolecular Engineering From the website of the Johns Hopkins University.
- ^ What is biomolecular engineering? From the website of Cornell University.
- ^ Department of Chemical and Biomolecular Engineering From the Tulane University website.
- ^ Chemical and Biomolecular Engineering From the University of Melbourne website.
- ^ The Changing Face of Chemical Engineering Chemical and Engineering News, June 4, 2001, a publication of the American Chemical Society.
- Milton Beychok