MRI is an acronym for Magnetic Resonance Imaging. MRI is used in radiology and it is one of the scanning technologies where magnetism, radio waves, and a computer are used to take the total image of the body structures. The chief advantage of the MRI is to give clear images of the soft-tissue structure where other imaging techniques fail to give without any effect to the patient.MRI is based on the interaction of magnetic properties of hydrogen with both a large external magnetic field and radio waves, which send signals to the body and then receive signals back. These returning signals are converted into images by a computer attached to the scanner. Imaging of any part of the body can be obtained in any plane. This Article gives a brief idea about the history, construction, working principle of MRI which includes Nuclear spin, Larmour,s frequency, T1 and T2 relaxation and T1 and T2 weighted images.