The Tissue is a cellular organizational level intermediate between cells and a complete organism. Hence, a tissue is an ensemble of cells, not necessarily identical, but from the same origin, that together carry out a specific function (in animals and plants). Organs are then formed by the functional grouping together of multiple tissues.

The classical tools for studying tissues are the paraffin block in which tissue is embedded and then sectioned, the histological stain, and the optical microscope. In the last couple of decades, developments in electron microscopy, immunofluorescence, and the use of frozen tissue sections have enhanced the detail that can be observed in tissues. With these tools, the classical appearances of tissues can be examined in health and disease, enabling considerable refinement of clinical diagnosis and prognosis.

The study of animal tissues is known as histology. Histology is the microscopic study of tissues of the animal and human bodies and how these tissues are organized to form organs (organogenesis). The word "histology" is derived from two Greek words, histo="tissue" and logos="study". The structure of tissues is so closely related to its function and vice versa. As gross anatomy shows you the picture of the body from outside, histology goes deep into the body to show you the microscopic features. In this way, students can correlate how microscopic structures are related with the gross structures.

Knowledge of tissue structure and function is important in understanding the structure and function of organs, organ systems, and the complete organism. Knowledge of histology also aids in understanding the pathology of tissues. This is because histology gives you the normal picture of a tissue while pathology discusses what changes occur in this normal tissue when it becomes abnormal or diseased. So, there is always a link between histology and pathology.

Undergraduate Student in Science Faculties.