The cell is the basic structural and functional unit of all known living organisms. It is the smallest unit of life that is classified as a living thing, and is often called the building block of life. Organisms can be classified as unicellular (consisting of a single cell; including most bacteria) or multicellular (including plants and animals). Humans contain about 10 trillion (10¹³) cells. Most plant and animal cells are between 1 and 100 µm and therefore are visible only under the microscope.

The cell was discovered by Robert Hooke in 1665. In 1835, before the final cell theory was developed, Jan Evangelista Purkyně observed small "granules" while looking at the plant tissue through a microscope. The cell theory, first developed in 1839 by Matthias Jakob Schleiden and Theodor Schwann, states that all organisms are composed of one or more cells, that all cells come from preexisting cells, that vital functions of an organism occur within cells, and that all cells contain the hereditary information necessary for regulating cell functions and for transmitting information to the next generation of cells.

Cell biology (formerly cytology, from the Greek kytos, "contain") is a scientific discipline that studies cells – their physiological properties, their structure, the organelles they contain, interactions with their environment, their life cycle, division and death. This is done both on a microscopic and molecular level. Cell biology research encompasses both the great diversity of single-celled organisms like bacteria and protozoa, as well as the many specialized cells in multicellular organisms such as humans.

Knowing the components of cells and how cells work is fundamental to all biological sciences. Appreciating the similarities and differences between cell types is particularly important to the fields of cell and molecular biology as well as to biomedical fields such as cancer research and developmental biology. These fundamental similarities and differences provide a unifying theme, sometimes allowing the principles learned from studying one cell type to be extrapolated and generalized to other cell types. Therefore, research in cell biology is closely related to genetics, biochemistry, molecular biology, immunology, and developmental biology.

Johns Hopkins (May 19, 1795 – December 24, 1873) was an American entrepreneur, abolitionist and philanthropist of 19th-century Baltimore, Maryland.

His bequests founded numerous institutions bearing his name, including Johns Hopkins Hospital, Johns Hopkins University, Johns Hopkins School of Nursing, Johns Hopkins School of Medicine, and Johns Hopkins Bloomberg School of Public Health.

A biography entitled Johns Hopkins: A Silhouette written by his cousin, Helen Hopkins Thom, was published in 1929 by the Johns Hopkins University Press.

Johns Hopkins was born on May 19, 1795, to Samuel Hopkins (1759–1814) of Anne Arundel County, Maryland, and Hannah Janney (1774–1864), of Loudoun County, Virginia. Home was Whitehall, a 500-acre (two km²) tobacco plantation in Anne Arundel County. His first name derives from a maternal great-grandmother, Margaret Johns, who passed it on to her son.

The Hopkins family were members of the Society of Friends (Quakers). In 1807 they emancipated their slaves in accordance with their local Society decree, which called for freeing the able-bodied and caring for the others, who would remain at the plantation and provide labor as they could. The second eldest of eleven children, 12 year-old Johns was required to work on the farm, interrupting his formal education. From 1806 to 1809, he likely attended The Free School of Anne Arundel County, which was located in today's Davidsonville, Maryland.