The process of innovation has shifted significantly over the past 40 years with teams becoming larger, more diverse, and more geographically dispersed. What are the sources and implications of the rise of teams and shifts in team composition? This paper quantifies the forces behind the rising importance of teams and, in so doing, builds a framework to evaluate the relative importance of specific innovative bundles expertise to a large economy of teams. I combine a tractable quantitative model with novel empirical measures on inventor and team expertise from the US Patent and Trademark Office (USPTO). In the model, inventors with heterogeneous expertise form teams weighing output produced, governed by an idea production function, against costs of forming and communicating in the team. The model delivers a sufficient statistic for valuing individual agent expertise. Empirically, I use measures of inventor and team expertise across patent technology classes to estimate the idea production function which responds to the team's \emph{depth}, expertise within the technological area, and \emph{breadth}, expertise outside the focal area, over time. I use geographical dispersion within teams to infer the costs of forming teams. I find that both changes in the returns to breadth and depth and falling communication costs explain a large share of the increase in team size, with increases in the returns to breadth and depth explaining over 50\% of this increase. These results have important and novel macroeconomic and policy implications. In particular, changes in the idea production function suggest an increasing importance for fostering complementary skills in teams. I perform counterfactuals where I shock the existing distribution of inventors with inflows of varying expertise and observe the corresponding general equilibrium changes in total innovative output. The overall outcome delivers qualitatively similar results to the sufficient statistic from the model and yields novel conclusions on optimal high-skilled immigration policy.