This is a theory of endogenous volatility over the business cycle based on firm-level intangible expenditures. We propose a firm dynamics model with endogenous market participation. Firms that incur higher intangible expenses are able to serve more markets and diversify market-specific demand risk. The model is driven only by TFP shocks and captures the business cycle properties of firm-level volatility and intangibles expenditures. We empirically document that firm-level volatility is counter-cyclical and that intangible expenses are pro-cyclical. Consistent with our model, using data from the Kauffman Firm Survey and Compustat, we find that firm-level idiosyncratic volatility is negatively correlated with intangible expenditures.