The article presents a study that is concerned with explaining the price of urban land during urbanization, with particular emphasis on its movement over time. Various characteristics of the land traded may explain its price in the cross section. Since, over time, the qualities of the land traded tend to change, the cross-section effects must be allowed for to disentangle the movement of prices over time. Theoretically, if the development of the land has been anticipated, the price of vacant land should tend to follow a time path determined by the discounting of its value at development at the prevailing interest rate. Changes in expectations, interest rates and holding costs, market imperfections, and short term construction requirements will lead to divergence of prices from the path. Relationships between land prices and relevant variables from the economy are to be anticipated. An empirical analysis of land prices in Northeast Philadelphia, Pennsylvania, tends to support the theoretical reasoning.