This paper sets up a monopolistic competition model featuring the returns to production specialization. Some novel results are derived from the analysis. First, the effect of a fiscal stimulus on consumption may be positive or negative, depending crucially upon whether the production function is characterized by increasing or decreasing returns to production specialization. Second, following a fiscal expansion, increasing returns to specialization lead to a positive linkage between real wages and aggregate output, while decreasing returns to specialization result in a negative relationship between real wages and aggregate output. Third, a fiscal expansion may raise social welfare, provided that the degree of increasing returns to production specialization is sufficiently large.