In genetics, a cDNA library is a set of strands of complementatary DNA (cDNA), that is, a DNA strand equivalent to a mRNA that is translated by ribosomes into protein. cDNA for a library can be generated from mRNA via reverse transcriptase.
Such a library has several uses. A cDNA of an eukaryotic organism (for example, a human) can be cloned into a prokaryotic organism (for example, E. coli) and expressed (translated into the appropriate protein) there (with limitations, for example posttranslational modification). A cDNA library is also important for analysis through bioinformatics. The complete cDNA library of an organism gives the total of the proteins it can possibly express. Also, the cDNA sequence gives the genetic relationship between organisms through the similarity of their cDNA.