Tissue differentiation is the process by which unspecialized cells develop into specialized cells that perform specific functions in an organism. This process is crucial during the development of multicellular organisms, allowing cells to form various types of tissues, such as muscle tissue, nervous tissue, and epithelial tissue. During differentiation, cells undergo changes in gene expression, leading to the development of unique structures and functions. For example, a stem cell can differentiate into a red blood cell or a neuron, depending on the signals it receives from its environment. This specialization is essential for the proper functioning of organs and systems within the body.