This paper describes some of the recent progress in Molecular Tagging Velocimetry and its applications. A brief overview of the different molecular tagging methods mostly in use today is given. Improvements in tagging, detection, and processing schemes, allow whole-field measurements of two components of the velocity vector simultaneously at more than 600 points over a plane with sufficient accuracy to make this technique a viable tool for fluid flow studies. Application of MTV to several flow

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... ields are described to highlight some of the capabilities of this technique. The examples include boundary-layer resolved measurements of unsteady boundary layer separation, slow convective flow in directional solidification, intake flow into a model IC engine, and the hot flow in late compression of a motored IC engine. Finally, examples are given to illustrate the potential for simultaneous flow visualization/passive scalar and velocity measurements, as well as threecomponent velocimetry using stereo imaging.