It is argued that insights can be gained by analyzing the use of urban growth boundaries for urban growth management as an inventory problem. The analysis provides three useful insights. First, it shows that where urban growth boundaries are employed, too much emphasis is placed on whether urban growth boundaries contain sufficient land to accommodate 20 years of growth and too little is placed on how frequently, how much or under what circumstances urban growth boundaries should be expanded. Second, it is shown that where market factors are used, they have been used inappropriately to increase the size of urban growth boundaries immediately after expansion, when they should be used to influence the size of urban growth boundaries immediately before expansion. Finally, it is shown that urban growth boundaries are likely to work better if expansions occur not after an arbitrary period of time but when the supply of land reaches some critical threshold.