A physicist is a scientist who specializes in the field of physics, which encompasses the interactions of matter and energy at all length and time scales in the physical universe. Physicists generally are interested in the root or ultimate causes of phenomena, and usually frame their understanding in mathematical terms. They work across a wide range of research fields, spanning all length scales: from sub-atomic and particle physics, through biological physics, to cosmological length scales encompassing the universe as a whole. The field generally includes two types of physicists: experimental physicists who specialize in the observation of natural phenomena and the development and analysis of experiments, and theoretical physicists who specialize in mathematical modeling of physical systems to rationalize, explain and predict natural phenomena.

भौतिक विज्ञानी अथवा भौतिक शास्त्री अथवा भौतिकीविद् वो वैज्ञानिक कहलाते हैं जो अपना शोध कार्य भौतिक विज्ञान के क्षेत्र में करते हैं। उप-परवमाणविक कणों से लेकर सम्पूर्ण ब्रह्माण्ड तक सभी परिघटनाओं का अध्ययन करने वाले लोग इस श्रेणी में माने जाते हैं।