Euroclast proposes a research training program on osteoclast biology in the context of osteoclast-driven diseases. Osteoclasts are the complex, multinuclear cells responsible for bone breakdown. Many diseases of osteoclast malfunctioning manifest in bone loss, for example, osteoporosis, cancer-induced bone disease, periodontitis, or rheumatoid arthritis, all conditions set to increase in an ageing EU population. The Euroclast consortium (7 academic, 2 private and 1 ass. partner) focuses on osteoclast heterogeneity, a recent insight that poses new fundamental questions best tackled by a multi-partner consortium capable of assembling the sophisticated molecular, genetic and imaging tools required. We will analyze changes in gene and protein expression during osteoclast (trans)differentiation from different precursor cell pools and in various bone sites and relate this to osteoclast activity and sensitivity to therapeutics. The osteoclast resorptiveapparatus will be studied using in depth and will define the key enzymatic and molecular machinery to be translated into novel site-specific drug targets or biomarkers. High throughput screening assays for therapeutics and ELISAs for biomarkers will be developed with our private partners. Our multidisciplinary and cross-sectorial approach will improve understanding and treatment of common disorders associated with osteoclast malfunction and train 11 early stage researchers (ESRs) in modern cell and bone biology. We will provide extensive training in generic skills and all ESRs will spend time with our private partners and be seconded to other academic partners to ensure they are well equipped for employment in research and industrial settings. Euroclast will produce an on-line repository for osteoclast protocols, make methodological and scientific advances in osteoclast and bone biology and create a sustainable network of ESRs and senior academics to tackle diseases of bone loss into the future.