Abstract: Over the past few decades, osteoblast differentiation has been studied extensively in a variety of culture systems and findings from these experiments have shaped our understanding of the bone-forming cell lineage. However, in vitro assays are bound by intrinsic limitations and are unable to effectively mirror many aspects related to osteoblasts in vivo, including their origin, destiny, and life span. Therefore, these fundamental questions strongly advocate the need for novel models to characterize the osteoblast lineage in vivo. Here, we developed a transgenic mouse system to study stage-specific subsets of osteoblast lineage cells. We believe that this system will prove to be a helpful tool in deciphering multiple aspects of osteoblast biology in vivo.