The function of CCDC66 (coiled-coil domain containing 66, ENSG00000180376) is as follows. Microtubule-binding protein required for ciliogenesis (PubMed:28235840). May function in ciliogenesis by mediating the transport of proteins like BBS4 to the cilium, but also through the organization of the centriolar satellites (PubMed:28235840). Required for the assembly of signaling-competent cilia with proper structure and length (PubMed:36606424). Mediates this function in part by regulating transition zone assembly and basal body recruitment of the IFT-B complex (PubMed:36606424). Cooperates with the ciliopathy proteins CSPP1 and CEP104 during cilium length regulation (PubMed:36606424). Essential for cilium elongation, maintaining ciliary length and stability, and inhibiting disassembly (likely by stabilizing the axoneme) (By similarity). Also plays a role in ciliary Hedgehog pathway activation (By similarity). Plays two important roles during cell division (PubMed:35849559). First, is required for mitotic progression via regulation of spindle assembly, organization and orientation, levels of spindle microtubules (MTs), kinetochore-fiber integrity, and chromosome alignment (PubMed:35849559). Second, functions during cytokinesis in part by regulating assembly and organization of central spindle and midbody MTs (PubMed:35849559). Plays a role in retina morphogenesis and/or homeostasis (By similarity). {ECO:0000250|UniProtKB:Q6NS45, ECO:0000269|PubMed:28235840, ECO:0000269|PubMed:35849559}.