Tissue engineering and regeneration tackled by methods to determine the state, movement, and fate of cells in vitro and in vivo revolutionized applied medicine. Thus, methods enabling imaging of cells at a single-cell as well as tissue level will be described in this chapter. The focus lies on optical methods and provides insights into technological limitations and methods that allow to break the diffraction limit. Beam scanning as well as widefield microscopy methods will be addressed. Non-optical imaging techniques are discussed in a more general term. A few exemplary publications will be briefly described for each discussed technology. The publications will provide further insights into newest applications, technological demands, and capabilities.