This paper explores Rosenstein-Rodan's (1943) idea that simultaneous industrialization of many sectors can be profitable for all of them, even when no sector can break even industrializing alone. The authors analyze this idea in the context of an imperfectly competitive economy with aggregate demand spillovers, interpreting the big push into industrialization as a move from a bad to a good equilibrium. They show that for two equilibria to exist, it must be the case that an industrializing firm raises the demand for products of other sectors through channels other than the contribution of its own profits to demand. For example, a firm paying high factory wages raises demand in other manufacturing sectors even if it loses money. In a similar vein, a firm investing today in order to produce at low cost tomorrow shifts income and hence demand for other goods into the future and so makes it more attractive for other firms also to invest today. Finally, an investing firm can benefit firms in other sectors if it uses a railroad or other shared infrastructure, and hence helps to defray the fixed cost of building the railroad. All these transmission mechanisms that help generate the big push seem to be of some relevance for less developed countries. The paper discusses the importance of domestic markets for industrialization, noting that even in open economies, domestic demand plays a crucial role. It presents a simple model of aggregate demand spillovers with a unique equilibrium, showing that individual investments can be unprofitable but still beneficial to other sectors. The authors also present a model with a factory wage premium, where higher wages in factories increase demand for other manufactured goods, even if the firm itself loses money. Another model focuses on the intertemporal aspect of industrialization, showing that investments made today can lead to higher future income and thus make industrialization more profitable. The paper also discusses the role of infrastructure investment, noting that shared infrastructure can reduce fixed costs and make industrialization more attractive. The authors conclude that the big push is a self-sustaining process that can lead to a Pareto improvement in the economy, and that government intervention can help accelerate this process.This paper explores Rosenstein-Rodan's (1943) idea that simultaneous industrialization of many sectors can be profitable for all of them, even when no sector can break even industrializing alone. The authors analyze this idea in the context of an imperfectly competitive economy with aggregate demand spillovers, interpreting the big push into industrialization as a move from a bad to a good equilibrium. They show that for two equilibria to exist, it must be the case that an industrializing firm raises the demand for products of other sectors through channels other than the contribution of its own profits to demand. For example, a firm paying high factory wages raises demand in other manufacturing sectors even if it loses money. In a similar vein, a firm investing today in order to produce at low cost tomorrow shifts income and hence demand for other goods into the future and so makes it more attractive for other firms also to invest today. Finally, an investing firm can benefit firms in other sectors if it uses a railroad or other shared infrastructure, and hence helps to defray the fixed cost of building the railroad. All these transmission mechanisms that help generate the big push seem to be of some relevance for less developed countries. The paper discusses the importance of domestic markets for industrialization, noting that even in open economies, domestic demand plays a crucial role. It presents a simple model of aggregate demand spillovers with a unique equilibrium, showing that individual investments can be unprofitable but still beneficial to other sectors. The authors also present a model with a factory wage premium, where higher wages in factories increase demand for other manufactured goods, even if the firm itself loses money. Another model focuses on the intertemporal aspect of industrialization, showing that investments made today can lead to higher future income and thus make industrialization more profitable. The paper also discusses the role of infrastructure investment, noting that shared infrastructure can reduce fixed costs and make industrialization more attractive. The authors conclude that the big push is a self-sustaining process that can lead to a Pareto improvement in the economy, and that government intervention can help accelerate this process.