Cholesterol is a vital lipid for mammalian life. It is essential for the structure of cell membranes, fetal development, and as a precursor for steroid hormones. However, in excess, cholesterol can be damaging to health. Thus, cellular cholesterol levels are under tight control. Previous research has focused on an early step in cholesterol synthesis: 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), target of the cholesterol-lowering class of drugs known as statins. However, there is a paucity of knowledge about the other regulatory steps in the pathway. In this thesis, we investigated 7-dehydrocholesterol reductase (DHCR7); the terminal enzyme of the Kandutsch-Russell pathway of cholesterol synthesis, which converts 7-dehydrocholesterol (7DHC) into cholesterol. A deficiency in DHCR7 causes the devastating developmental disease Smith-Lemli-Opitz syndrome, highlighting the importance of the enzyme in cellular growth and development. Here, we show that DHCR7 is regulated via multiple mechanisms. At the transcriptional level, regulation occurs through dual sterol regulatory elements within the human DHCR7 promoter, which work cooperatively to control gene expression. These findings supersede previous work into the promoter of rat Dhcr7, which we have found has evolved into a more sophisticated regulatory system in higher organisms. At the post-translational level, we discovered that cholesterol induces the proteolytic degradation of DHCR7 protein. This results in the subsequent accumulation of its substrate 7DHC, which is also the precursor for vitamin D. Thus, the degradation of DHCR7 switches flux away from cholesterol synthesis into vitamin D production. Finally, we explored the role of signaling in DHCR7 regulation and identified that phosphorylation acutely controls DHCR7 activity, at a known phosphorylation site, S14. We found that inhibition of AMP-kinase and protein kinase A also ablated DHCR7 activity, through an unknown phosphorylation site. This loss of DHCR7 activity also has the potential to promote flux into vitamin D synthesis. Overall, these findings indicate that DHCR7 is an important regulatory step in cholesterol and vitamin D synthesis, playing a critical role in the homeostasis of two important molecules that are involved in human health and disease.