Osteoclasts are bone-digesting cells essential for regulation of skeletal bone mass and underscore pathologies such as osteoporosis and osteopetrosis. These multinucleated giants arise from the asynchronous fusion of mononuclear cells of the monocyte-macrophage lineage in response to pro-osteoclastogenic cytokines M-CSF and RANKL. Upon attachment to bone, osteoclasts adopt a polarised conformation signified by the formation of the ruffled border membrane, the osteoclast’s giant extracellular ‘bone-resorbing organelle’. This highly convoluted apparatus shares close analogies with endolysosomal and autophagic membranes and has long been considered to arise from the fusion of globular ‘secretory lysosomes’ with the bone-facing plasmalemma. Recently, using advanced live cell microscopy, we found that rather than simply existing as globular organelles, osteoclast secretory lysosomes rearrange into an expansive tubular network that services ruffled border. By combining organelle-level proteomics together with high-resolution microscopy and genetic studies in mice we recently resolved the molecular inventory of osteoclast secretory lysosomes and unmasked several new regulators that are indispensable for osteoclast function, lysosome tubulation, and the maintenance of skeletal bone mass. This presentation will disclose emerging evidence that the osteoclast’s specialised lysosome-related organelles are far more complex than previously envisaged and demonstrate the utility of these unique bone-digesting giants as a model system for studying tubular lysosomes.