Magnetic resonance imaging with its superior soft tissue contrast resolution and absence of beam hardening artifacts, combined with its ability to perform multiplanar imaging, is now effective tool in diagnostic imagings. Magnetic resonance is primarily a phenomenon that involves atomic nuclei. It provides totally new clinical informations with no known hazards through the use of very weak interactions with endogenous stable magnetic atomic nuclei. This article briefly summarizes the basic mechanism of generation and detection of the signals and general sorts of tissue properties which can influence the signals and thereby give rise to tissue contrast. It also describes how the machine-operating parameters can be used to manipulate the tissue contrast observed in the image.