The present invention provides compositions, kits, assemblies, libraries, arrays, and high throughput methods for large scale structural and functional characterization of gene expression regulatory elements in a genome of an organism, especially in a human genome. In one aspect of the invention, an array of expression constructs is provided, each of the expression constructs comprising: a nucleic acid segment operably linked with a reporter sequence in an expression vector such that expression of the reporter sequence is under the transcriptional control of the nucleic acid segment, the nucleic acid segment varying in the library and having a diversity of at least 50. The nucleic acid segments can be a large library of gene expression regulatory elements such as transcriptional promoters. The present invention can have a wide variety of applications such as in personalized medicine, pharmacogenomics, and correlation of polymorphisms with phenotypic traits.