The cell theory is the guiding doctrine about cells and living organisms. It states that all living organisms are made up of one or more cells and that growth and development results from the division and differentiation of cells. This makes the cell the basic structural unit of life. Cell Theory traces the history of the development of the cell theory, which was first proposed almost 200 years ago, from the discovery of the cell through the investigations used to prove its accuracy. Today, scientists almost universally accept the cell theory. Readers will gain valuable knowledge about this scientific concept, helping them understand this life science topic.