COP1 and DET1 are among the first repressors of photomorphogenesis to be identified, more than 20 years ago. Discovery of these repressors as conserved regulators of the ubiquitin-proteasome system has established protein degradation as a central theme in light signal transduction. COP1 is a RING E3 ubiquitin ligase that targets key regulators for degradation, and DET1 complexes with COP10 and DDB1, which is proposed to aid in COP1-mediated degradation. Recent studies have strengthened the role of COP1 as a major signaling center. DET1 is also emerging as a chromatin regulator in repressing gene expression. Here, we review current understanding on COP1 and DET1, with a focus on their role as part of two distinct, multimeric CUL4-based E3 ligases.