Diffusion curve analysis can estimate whether an innovation spreads endogenously (indicated by a characteristic "s-curve") or exogenously (indicated by a characteristic negative exponential curve). Current techniques for pooling information across multiple innovations require a two-stage analysis. In this paper, we develop multilevel diffusion curve analysis, which is statistically more efficient and allows for more flexible specifications than do existing methods. To substantively illustrate this technique, we use data on bribery in pop radio as an example of exogenous influence on diffusion. Copyright © 2008 by American Sociological Association.