This course explains the basic principles of optical interferometry applied to biological problems and systems. Interference is at the core of many types of optical detection and is a powerful probe of cellular and tissue structure such as for interference microscopy and optical coherence tomography. Interference is also the root cause of speckle and other imaging artifacts that limit range and resolution. Furthermore, the inherent sensitivity of interferometry enables ultrasensitive detection of molecules in biological samples for medical diagnostics using biosensors. In this course, emphasis is placed on the physics of light scattering, with a focus on coherence detection techniques that allow information to be selectively detected out of incoherent and heterogeneous backgrounds. <p> </p>Bio-Interferometry is divided into four parts. The first part covers fundamental principles of partial coherence and interferometry. The next three parts move up successive size scales: biosensors and molecular interferometry (nano-scale), cellular interferometry and microscopy (micron-scale), and ending with tissue interferometry and holography (millimeter scale). The course clearly presents the physics, with easy derivations of the appropriate equations, while emphasizing "rules of thumb" that can be applied by experimental researchers to give semi-quantitative predictions.