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Histology is the branch of biology that studies the microscopic structure of tissues. It connects cellular organization to the function of organs and systems, complementing cytology in the broader field of anatomy. Histology analyzes how cells and the extracellular matrix are arranged, interact, and contribute to tissue properties.

Standard methods in histology involve fixation to preserve tissue architecture, dehydration and embedding in paraffin or resin, and thin sectioning with a microtome. Sections are mounted on slides and stained to reveal details. The most common stain is hematoxylin and eosin, which highlights nuclei and cytoplasm, respectively. Modern histology also employs immunohistochemistry, special stains, and electron microscopy to explore molecular composition and ultrastructure.

In animals, four basic tissue types are studied: epithelial tissue (covering and lining surfaces and forming glands), connective tissue (support and binding, including bone and blood), muscle tissue (skeletal, smooth, and cardiac), and nervous tissue (neurons and glia). These tissues combine to form organs and contribute to organ systems through specialized architecture and function.

Histology underpins pathology and diagnostic medicine by revealing tissue organization and abnormalities. It also supports basic biological research, developmental studies, pharmacology, and education. Histological techniques are documented in comprehensive atlases and increasingly complemented by digital imaging and whole-slide scanning for teaching and remote consultation.

Historically, histology developed with the advancement of microscopy in the 19th century, aided by tissue staining methods that improved visualization of cellular structures. Today, histology integrates molecular techniques and imaging to study tissue structure, composition, and function at multiple scales.