This report is an abridged and revised English language edition of the original proposition of the Finnish restoration prioritization working group on the options and costs of restoring 15 percent of degraded ecosystems in Finland. We start with the key findings and the original propositions of the working group. Based on the experiences from Finland, we also provide a few new propositions for the international readership to help to plan and implement work towards meeting the global target of restoring 15 percent of the degraded ecosystems. In the beginning of the report, we describe the conceptual background of the work, i.e. that ecosystem degradation or improvement has a minimum of two components: the extent of area that has become degraded or restored and the magnitude of the degradation, or its counterpart improvement, at any given location. We then describe the procedure that we developed to systematically measure the magnitude of degradation from which the 15 percent can be calculated and the magnitude of improvement that different restoration measures can offer. The guiding principle adopted for the development of the procedure was to treat all ecosystems that are not in their natural state as degraded. However, it is worth emphasizing that the objective is not to reach the natural state of the ecosystems, but to reduce the degree of ecosystem degradation by restoration. With an example from herb-rich forests, we show how we prioritized restoration measures within an ecosystem. The prioritization was based on the effects of restoration measures on biodiversity and on the costs of the measures. We also considered the effect of restoration measures on some key ecosystem services. In addition to the restoration measures within each ecosystem, we also conducted prioritization among ecosystems. The prioritization among ecosystems is based on an analysis identifying the ecosystems where reasonable investments bring the greatest reduction in the degree of ecosystem degradation. The procedure thus enabled us to find the balanced and cost-effective restoration measure portfolios within each ecosystem type and to allocate resources effectively to those ecosystem types that provided highest benefits in terms of biodiversity and reduction of the degree of ecosystem degradation. To our knowledge, this report is the first to estimate the cost of meeting the 15 percent restoration target across all relevant terrestrial ecosystems in one country. Our work exemplifies that simultaneous prioritization among all major terrestrial ecosystems greatly reduces the overall cost of meeting the 15 percent restoration target. Indeed, if we focus on restoring 15 per cent of one ecosystem type at a time, which is the modus operandi in many parts of the world, the overall cost of meeting the 15 percent restoration target is more than twice compared to the prioritization approach we have adopted here. Rather than getting fixed on the 15 percent target, we also decided to provide additional options for decision makers. Thus, the report gives alternative answers to the question of which ecosystem restoration measures to take, at which scale and in which ecosystem types, in order to meet the overall target for ecosystem restoration in Finland.