Alfred Day Hershey was born December 4, 1908 in Owosso, Michigan. He received his B.S. in 1930 and his Ph.D. in 1934 from Michigan State University. Hershey then served on the faculty in the Department of Bacteriology at the Washington University School of Medicine in St. Louis from 1934 to1950. Hershey's early research at Washington University was on the growth and metabolism of bacteria, the infectivity of bacterial viruses, bacteriophages, and the immunological interactions of antibodies with bacteriophages. From these interests Hershey went to play a key role in the development of phages as productive systems for the exploration of the molecular basis of biology.

In 1950, he joined the staff of the Genetics Research Unit, Carnegie Institution of Washington at Cold Spring Harbor, where he served as Director from 1962 until his retirement in 1974.

Hershey is best known for his work at Cold Spring Harbor with Martha Chase, studying the contributions of the nucleic acid and protein components of phage particles to heredity. Hershey and Chase labeled the proteins the deoxyribonucleic acid (DNA) of phage particles with radioactive tracers and allowed these double-labeled phages to infect E. coli. A short time later, the culture was vigorously mixed with a high-speed blender. The phage proteins were sheared from the bacterial cell, but the DNA remained associated with the bacteria continued to program the complete development of progeny phages. Hershey and Chase concluded that the role of the proteins was to encapsulate and protect the DNA, to attach to sensitive bacteria, and to inject DNA into the host. The DNA, on the other hand, was the material basis for heredity, encoding each genetic characteristic as well as the program for the growth and development of progeny. This work was central to Hershey's receiving the 1969 Nobel Prize in Physiology or Medicine.

Hershey's laboratory extended these studies to demonstrate that viral growth occurs in two stages: the replication of the nucleic acid and the synthesis of capsid proteins and their assembly in mature progeny phage particles. He also examined the biophysical properties of DNA, showing that the molecular of heredity was an extremely long polymer but of discrete and homogeneous size for a given phage. His lab developed the means to measure the molecular weights of long DNA molecules, to break them in controlled ways, and to fractionate the pieces. He discovered the cohesive ends that allow lambda phages to circularize, forming molecules that have come to be known as "Hershey circles." Throughout these investigations, Alfred Hershey brought quiet elegance to three decades of phage research.

Hershey was elected to the National Academy of Sciences in 1958 and to the American Academy of Arts and Sciences in 1959. He received the Albert Lasker Award of the American Public Health Association in 1958 and the Kimber Genetics Award of the National Academy of Sciences in 1965. Hershey shared the 1969 Nobel Prize for Physiology or Medicine with Professor Max Delbrück and Professor Salvador Luria.

During his life, Hershey published more than 100 articles in scientific journals and books and was the principal editor of the important reference book Bacteriophages (by Mark H. Adams, completed after the author's death) and the highly regarded book The Bacteriophage Lambda, published by Cold Spring Harbor Laboratory Press. Hershey's many review articles on phage genetics and molecular biology have been an enduring source of education, guidance, and insight. His personal example and creative interactions with innumerable colleagues gave focus and an extra measure of rigor to the developing field.

Hershey died at his home, in the village of Laurel Hollow, New York on May 22, 1997 at the age of 88.