Short Tandem Repeat (STR) analysis is a molecular biology method used to compare allele repeats at specific loci in DNA between two or more samples. STRs are short sequences of DNA, normally of length 2-5 base pairs, that are repeated numerous times in a head-tail manner, and the polymorphisms in STRs are due to the different number of copies of the repeat element that can occur in a population of individuals. STR analysis is a tool in forensic analysis that evaluates specific STR regions found on nuclear DNA, and the variable (polymorphic) nature of the STR regions that are analyzed for forensic testing intensifies the discrimination between one DNA profile and another. In the United States, 13 autosomal STR loci are now accepted as the system used for forensic purposes, and given a robust crime scene DNA sample with good data for all 13 STRs, the likelihood of a person unrelated to the actual person who committed the crime having a perfect match for all 13 is typically around 1 in 1 billion. STR analysis is also used in paternity testing and to establish identity of missing persons.

It is important to note that the term "STR" can also refer to short-term rental (STR) real estate, which is generally defined as property that is rented for fewer than 31 days to the same tenant.