Damaged DNA Binding Protein 1 (DDB1) – CULLIN4 E3 ubiquitin ligase complexes have been implicated in a variety of biological processes in a range of organisms. Uniquely, Arabidopsis thaliana encodes two homologs of DDB1, DDB1A and DDB1B. In this study we utilize a viable partial loss of function allele of DDB1B, ddb1b-2, to examine genetic interactions with DDB1A, DET1 and COP1. While the ddb1b-2 ddb1a double mutant is lethal, ddb1a ddb1b-2/+ and ddb1b-2 ddb1a/+ heterozygotes do not exhibit any developmental phenotypes. These heterozygotes do however exhibit decreased UV tolerance. In addition, germination in ddb1a and ddb1a ddb1b-2/+ was found to be sensitive to salt and mannitol, and both DDB1 single mutants as well as the heterozygotes exhibited heat sensitivity. DE-ETIOLATED1 (DET1) and CONSTITUTIVE PHOTOMORPHOGENIC1 (COP1) are negative regulators of light development which interact with DDB1A. While ddb1a enhances det1 phenotypes in both dark and light grown seedlings, ddb1b-2 did not affect det1 dark phenotypes but enhanced anthocyanin levels and suppressed the det1 low chlorophyll phenotype in light grown seedlings. In adults, ddb1a suppresses det1 early flowering and enhances the det1 dwarf phenotype. A similar trend was observed in ddb1b-2 det1 double mutants, although the effects were smaller in magnitude. In cop1 mutants, ddb1b-2 enhanced the cop1-4 short hypocotyl phenotype in the dark, and enhanced anthocyanin levels and suppressed the short hypocotyl phenotype in cop1-1 in the light, but had no effect in adults. Hence DDB1B and DDB1A vary in their importance to different complexes during development.