在分子生物学中, 一个基因文库是通过分子克隆的方法存储和繁殖微生物群的DNA片段的集合。 存在不同种类的基因文库，包括部分基因文库（cDNA文库）、基因组文库（由基因组DNA形成），以及随机突变体库(由被替代的核苷酸或密码子结合形成的新的基因合成)。基因文库是当前分子生物学的一个主要研究方向 ，这些库的用途取决于原始DNA片段的来源。克隆载体和基因库准备的技术存在区别，但通常来说每个DNA片段都被独立地插入一个克隆载体然后重组DNA转化入受体菌（细菌人工染色体或BAC库）或酵母内，使得每个生物体平均含有一个构建的表达载体 (载体 + 插入)。 随着培养的种群的数量的增长，其中包含的DNA也在被复制。

In molecular biology, a library is a collection of DNA fragments that is stored and propagated in a population of micro-organisms through the process of molecular cloning. There are different types of DNA libraries, including cDNA libraries (formed from reverse-transcribed RNA), genomic libraries (formed from genomic DNA) and randomized mutant libraries (formed by de novo gene synthesis where alternative nucleotides or codons are incorporated). DNA library technology is a mainstay of current molecular biology, and the applications of these libraries depends on the source of the original DNA fragments. There are differences in the cloning vectors and techniques used in library preparation, but in general each DNA fragment is uniquely inserted into a cloning vector and the pool of recombinant DNA molecules is then transferred into a population of bacteria (a Bacterial Artificial Chromosome or BAC library) or yeast such that each organism contains on average one construct (vector + insert). As the population of organisms is grown in culture, the DNA molecules contained within them are copied and propagated (thus, "cloned").