Abstract: This article analyzes concerns about market power and inequality in a model with multiple sectors, heterogeneous abilities, endogenous labor supply, and nonlinear income taxation. Proportional markups with no profit dissipation have no effect on the economy, and a policy that reduces a nonproportional markup raises (lowers) welfare when it is higher (lower) than a weighted average of other markups. With proportional (partial or full) profit dissipation, proportional markups are equivalent to a downward shift of the distribution of abilities, and the optimal policy rule with nonproportional markups maximizes consumer plus producer surplus despite concerns for distribution and labor supply distortion.