Erwin Chargaff (August 11, 1905 - June 20, 2002) was an Austrian chemist. Chargaff was born in Czernowitz, Bukowina, Austria. From 1923-1928, Chargaff studied chemistry in Vienna, then two years in Yale. From 1930 on he worked at the University of Berlin, until he switched to the Pasteur Institute in Paris in 1933. In 1935 he emigrated to New York. Chargaff became a professor at Columbia University.

Edwin Chargaff proposed two main rules in his lifetime which were appropiately named 'Chargaff's rules'. The first and best known achievement was to show that in any double-stranded DNA the number of guanine units equals the number of cytosine units and the number of adenine units equals the number of thymine units. In human DNA, for example, the four bases are present in these percentages: A=30.9% and T=29.4%; G=19.9% and C=19.8%. This strongly hinted towards the base pair makeup of the DNA. Although Chargaff did not offer any explanation for his results and refused to speculate, it was clear that they were not in accordance with Watson's like-with-like model which he regarded as being 'unsound'. This discovery helped Watson and Crick in their discovery of the [double helical structure of DNA.] The second is that the composition of DNA varies from one species to another, in particular in the relative amounts of A,G,T and C bases. Such evidence of molecular diversity, which had been presumed absent from DNA, made DNA a more credible candidate for the genetic material than protein.

He is also credited with disproving the tetranucleotide hypothesis. Given that the Rockefeller biochemist Phoebus Levene 's tetranucleotide hypothesis (that DNA was composed of a large number of repeats of GACT) was generally accepted, most workers assumed that deviations from equimolar base ratios were due to experimental error. Chargaff documented that the variation was real, with [C + G] typically being slightly less abundant. He was able to do this with the newly developed paper chromotography and ultraviolet spectrophotometer. He met Francis Crick and James Watson at Cambridge in 1952, and despite not getting on well with them personally, explained his findings to them.

He also noted that 80% of purines and pyrimidines in DNA were found in 'tracts' or runs of 3 or more bases, that the GC content of DNA was characteristic for an organism and that within single strands of DNA - to a very good approximation - A = T and C = G .