In all vertebrates, the genes encoding Antigen Receptor (AgR) variable (V) regions are assembled during B and T cell development from gene segments termed V, (D), and J through the process of V(D)J recombination. V(D)J recombination is central for the successful function and development of B and T cell lymphocytes. Recombination Activating Gene 1 (RAG1) and RAG2 are the essential and tissue specific components of V(D)J recombination. Their precise pattern of expression during B and T cell development determines where and when V(D)J recombination occurs. This thesis describes studies on the regulation of RAG1 and RAG2 at the transcription level. In chapter 2, I have characterized the exon 1 and promoter region of human RAG1. I show that a single promoter region is used for RAG1 transcription. In chapter 3, I describe the isolation and characterization of the human RAG2 promoter regions. The major transcription initiation site (exon 1A) of human RAG2 is located 3.9 kb upstream of the coding exon while the less frequently used transcription initiation site (exon 1B) is only 0.7 kb upstream of the coding exon. Two alternate promoters upstream of exon1A or 1B drive the transcription of RAG2 gene. Using transient assays, I show that promoter regions of human RAG1 and RAG2 are active in both lymphoid and non-lymphoid cell lines. Chapter 4 describes an approach that I took to study the tissue-specific regulation of RAG genes. I stably transfected a 65 kb P1 phage genomic clone containing RAG1, RAG2 and their surrounding sequences, into the human cervical carcinoma cell line, HeLa (RAG1-, RAG2-) and the mouse pre-B cell line, NFS-70 (RAG1+, RAG2+). I found consistent expression of the human RAG1 gene in multiple clones of NFS-70 cell line while no RAG1 expression was detected in HeLa clones suggesting that this genomic clone contains some of the sequences required for the tissue-specific regulation of RAG1. In chapter 5, I describe the second approach to isolate the potential regulatory elements by subcloning fragments of the P1 phage into the RAG1 promoter construct and subsequently looking for enhancer or silencer activity. I located a 1425 bp within the 3' untranslated region of the RAG1 gene with enhancer activity. In chapter 6, I describe the subcloning and sequencing a 7.3 kilobase of the 5' flanking region of human RAG2 to look for potential conserved regulatory elements between human and mouse species. In Chapter 7, models of RAG1/RAG2 promoters, and their tissue-specific transcriptional regulation are discussed.