If a temporary need to quickly deliver new units justifies a subsidy, then it is logical for any subsidy to be temporary and for its size to be based on the number of housing units created, not on the value of units in the project. Moreover, because a subsidy can be justified in theory does not imply that any subsidy program is justifiable. A specific subsidy policy makes sense only if its benefits exceed its costs. Consequently, the primary purpose of this report is to analyze the effective cost per new unit built of different possible tax abatement programs. This report’s authors feel confident in assessing these costs, but they stress that only Boston’s leaders have the standing to decide how much they are willing to pay, in terms of foregone taxes, to produce more housing quickly. This report provides those leaders with estimates of the number of additional units gained and the cost of providing those units through different subsidy policies. These costs must be weighed against the social value that the City of Boston places on the immediate production of additional housing.