Oligonucleotides (or oligos) are small nucleic acid polymers, usually less than 20 bases in length. Oligonucleotides can be made by enzymatic cleavage or more commonly via chemical synthesis with polymerases. Oligos have a number of uses from research to disease diagnosis and recently therapeutics. The wide availability of affordable synthetic single-stranded DNA and RNA has opened the way for routine DNA amplification by PCR. This use of oligonucleotides as primers has revolutionized the study of gene expression and disease processes. Apart from their use as PCR primers, oligonucleotides are used as probes, in situ hybridization, in microarray, and antisense analyses, and even as drug carriers.