Our lungs are beautifully designed and energetically efficient gas-exchange systems that are formed by complex, tree-like networks. However, sometimes lungs do not form correctly during embryonic development, leading to abnormal function and—in some cases—infant mortality. There is therefore a pressing clinical need to understand how the lung forms. Here, I studied how branches in the developing lung elongate into their final shape. Specifically, I examined the mechanical interactions that sculpt branches, similar to how a sculptor molds clay into its final form. There is existing evidence that focal adhesions—which act like feet that tether cells to nearby extracellular matrix—play a role in the mechanical processes that shape branches. To better understand these mechanisms, I disrupted focal adhesion signaling in embryonic mouse lungs and observed resulting patterns in tissues surrounding the branches. I found that focal adhesion signaling controls the distribution of extracellular structural proteins and smooth muscle that wraps around the surface of the branches. These patterns tune the mechanical properties of lung tissue that ultimately lead to changes in organ shape. My work represents a step toward understanding how our lungs form in an effort to develop clinical interventions that will combat congenital birth defects in the lung.