**Abstract**

Cell culture is one of the most important and commonly used *in vitro* tools to comprehend various aspects of cells or tissues of a living body such as cell biology, tissue morphology, mechanism of diseases, cell signaling, drug action, cancer research and also finds its great importance in preclinical trials of various drugs. There are two major types of cell cultures that are most commonly used- two-dimensional (2D) and three-dimensional culture (3D). The former has been used since the 1900s, owing to its simplicity and low-cost maintenance as it forms a monolayer, while the latter being the advanced version and currently most worked upon. This chapter intends to provide the true meaning and significance to both cultures. It starts by making a clear distinction between the two and proceeds further to discuss their different applications *in vitro*. The significance of 2D culture is projected through different assays and therapeutic treatment to understand cell motility and treatment of diseases, whereas 3D culture includes different models and spheroid structures consisting of multiple layers of cells, and puts a light on its use in drug discovery and development. The chapter is concluded with a detailed account of the production of therapeutic proteins by the use of cells.

**Keywords:** Cell culture, 2D culture, 3D culture, drug action, therapeutics
