Alexander Solomon Wiener (March 16, 1907 – November 6, 1976) was an American biologist and physician, specializing in the fields of forensic medicine, serology, and immunogenetics. His work led to the discovery of the Rh factor in 1937, along with Karl Landsteiner, and subsequently to the development of exchange transfusion methods that saved the lives of infants with hemolytic disease of the newborn. He received a Lasker Award for his achievement in 1946.

Alexander Solomon Wiener was born in Brooklyn, New York, the son of George Wiener, an attorney who had emigrated from Russia in 1903, and Mollie (Zuckerman) Wiener. He attended Brooklyn public schools, graduating from Brooklyn Boys' High School at the age of 15. He was awarded scholarships to attend Cornell University where he continued his study of mathematics and even contributed mathematical problems to the American Mathematical Monthly. He majored in biology, however, receiving his A.B. in 1926. He then entered the Long Island College of Medicine where he was awarded an M.D. in 1930.

During his time in medical school Wiener did research work on blood groups at the Jewish Hospital of Brooklyn and from 1930 to 1932 he interned there and kept up a lifelong affiliation with that institution as the head of the Division of Genetics and Biometrics (1933–1935) and as the head of the blood transfusion division until 1952. From 1932 he had a medical practice and in 1935 he founded the Wiener Laboratories for clinical pathology and blood grouping. In 1938 he became a member of the Department of Forensic Medicine of New York University School of Medicine, rising to the rank of professor by 1968. From the 1930s he co-operated with the office of the Chief Medical Examiner of New York City.

Wiener was a good pianist and enjoyed tennis and golf. He kept up his lifelong interest in mathematics and physics by reading in these areas. In recognition of his contribution to forensic medicine he was awarded an honorary membership of the Mystery Writers of America.

In 1932 Wiener married Gertrude Rodman and they had two daughters, Jane and Barbara. Wiener died of leukemia in New York on November 6, 1976.

Wiener began working with Landsteiner at the age of 23, shortly after beginning his work at Brooklyn Jewish Hospital, where he remained for the rest of his life. Much of their initial work revolved around the M Factor, which they discovered was actually five different, distinct blood factors.

This encouraged them in their quest to create a blood "fingerprint," a unique blood profile that could be used in legal and criminal matters. Wiener pioneered much of the type of blood testing that has now, in the age of DNA, become commonplace. Along with his work in his Brooklyn lab, Wiener also did a considerable amount of work in a Manhattan lab where he concentrated on forensics, assisting the police in numerous investigations by analyzing the blood (or related fluids) of those involved.

Numerous articles and chapters of books with real life crime stories were written about Dr. Wiener's work in criminology. Along with his father, George Wiener, a lawyer. Wiener helped draft a new set of laws addressing the recent scientific advancements in blood identification. He was a member of the American Medical Association legal committee that sponsored blood test laws in all states, and he was the co-author of its 1935 report. His work in the genetics of the blood factors also allowed him to be of assistance in many paternity cases.