Human osteoclasts were differentiated using receptor activator of NFκB ligand (RANKL) and macrophage colony stimulating factor (M‐CSF) from colony forming unit‐granulocyte macrophage (CFU‐GM) precursors of the myeloid lineage grown from umbilical cord blood. Gene expression profiling using quantitative polymerase chain reaction (Q‐PCR) showed more than 1,000‐fold induction of chemokine MCP‐1 within 24 h of RANKL treatment. MCP‐1 mRNA content exceeds that of other assayed chemokines (CCL1, 3, 4, and 5) at all time points up to day 14 of treatment. MCP‐1 induction preceded peak induction of calcium signaling activator calmodulin 1 (CALM1) and transcription factors JUN and FOS, which were at 3 days. Key osteoclast related transcription factors NFATc1 and NFATc2 showed peak induction at 7 days, while marker genes for osteoclast function cathepsin K and tartrate resistance acid phosphatase (TRAP) were maximally induced at 14 days, corresponding with mature osteoclast function. To test whether the early and substantial peak in MCP‐1 expression is part of human osteoclast differentiation events, a dominant negative inhibitor of MCP‐1 (7ND) was added simultaneously with RANKL and M‐CSF, resulting in blockade of CALM1, JUN and NFATc2 induction and strong inhibition of human osteoclast differentiation. These data show that a cascade of gene expression leading to osteoclast differentiation depends on intact early MCP‐1 induction and signaling in human osteoclasts.