Steven M. Block (born 1952) is an American biophysicist and Professor at Stanford University with a joint appointment in the departments of Biology and Applied Physics.

In addition, he is a member of the scientific advisory group JASON, a senior fellow of Stanford's Freeman Spogli Institute for International Studies, and an amateur bluegrass musician.

He has been elected to the U.S. National Academy of Sciences (2007) and the American Academy of Arts and Sciences (2000) and is a winner of the Max Delbruck Prize[1] of the American Physical Society (2008), as well as the Single Molecule Biophysics Prize of the Biophysical Society (2007).

As an independent scientist, Block has pioneered the use of optical tweezers, a technique developed by Arthur Ashkin, to study biological enzymes and polymers at the single-molecule level.

[3] While consulting for the United States government through JASON, Block has researched the many threats associated with bioterrorism and headed influential studies on how advances in genetic engineering have impacted biological warfare.