This chapter discusses physical principles and clinical applications of tissue Doppler and strain imaging. Tissue Doppler imaging (TDI) and strain imaging are two of the several disruptive technologies which may objectively show degree, type and rate of regional and global myocardial function at specific points in the cardiac cycle. These two methods have prime-time utility in evaluation of global and segmental myocardial mechanical behavior in clinical situations with certain caveats. This chapter covers the mechanical structure and behavior of the heart muscle, architecture and function of myocardium, myocardial form and function, descriptive terms, labeling of tissue velocity waveforms, concept of tissue Doppler imaging, technical details of tissue Doppler imaging, myocardial velocities in short axis, internal dependency of velocities, clinical applications of TDI, effects of ischemia on regional deformation metrics, and early systolic longitudinal lengthening (paradoxical longitudinal systolic strain).