The Scenario Model Intercomparison Project (ScenarioMIP) is a key activity within Phase 6 of the Coupled Model Intercomparison Project (CMIP6), providing multi-model climate projections based on alternative scenarios of future emissions and land use changes. These scenarios are generated using integrated assessment models (IAMs) based on the Shared Socioeconomic Pathways (SSPs) and related to the Representative Concentration Pathways (RCPs). ScenarioMIP aims to facilitate integrated research across climate science, IAM, and impacts, adaptation, and vulnerability communities, and will form an important part of the evidence base for the upcoming Intergovernmental Panel on Climate Change (IPCC) assessments. It will also provide a basis for investigating targeted science and policy questions, including the role of specific forcings, the effect of a peak and decline in forcing, and the consequences of scenarios that limit warming to below 2°C. The design includes eight 21st century scenarios plus one large initial condition ensemble and a set of long-term extensions, divided into two tiers by priority. These scenarios will be used to address a wide range of scientific questions, including the effects of different forcing pathways on climate outcomes, the sensitivity of climate outcomes to SSP choices, and the feasibility of scenarios in the real world. ScenarioMIP simulations will also help test emergent constraints and explore the potential of climate model emulators to produce climate outcomes for forcing pathways not represented in the design. The design includes updated RCPs based on SSPs and new "gap" scenarios to address new questions of interest for integrated analysis. The scenarios are arranged into two tiers, with Tier 1 covering a wide range of uncertainty in future forcing pathways and providing key scenarios to anchor experiments in other MIPs. Tier 2 includes additional scenarios, ensemble members, and long-term extensions. The design aims to provide a comprehensive set of scenarios to support climate research and policy discussions.The Scenario Model Intercomparison Project (ScenarioMIP) is a key activity within Phase 6 of the Coupled Model Intercomparison Project (CMIP6), providing multi-model climate projections based on alternative scenarios of future emissions and land use changes. These scenarios are generated using integrated assessment models (IAMs) based on the Shared Socioeconomic Pathways (SSPs) and related to the Representative Concentration Pathways (RCPs). ScenarioMIP aims to facilitate integrated research across climate science, IAM, and impacts, adaptation, and vulnerability communities, and will form an important part of the evidence base for the upcoming Intergovernmental Panel on Climate Change (IPCC) assessments. It will also provide a basis for investigating targeted science and policy questions, including the role of specific forcings, the effect of a peak and decline in forcing, and the consequences of scenarios that limit warming to below 2°C. The design includes eight 21st century scenarios plus one large initial condition ensemble and a set of long-term extensions, divided into two tiers by priority. These scenarios will be used to address a wide range of scientific questions, including the effects of different forcing pathways on climate outcomes, the sensitivity of climate outcomes to SSP choices, and the feasibility of scenarios in the real world. ScenarioMIP simulations will also help test emergent constraints and explore the potential of climate model emulators to produce climate outcomes for forcing pathways not represented in the design. The design includes updated RCPs based on SSPs and new "gap" scenarios to address new questions of interest for integrated analysis. The scenarios are arranged into two tiers, with Tier 1 covering a wide range of uncertainty in future forcing pathways and providing key scenarios to anchor experiments in other MIPs. Tier 2 includes additional scenarios, ensemble members, and long-term extensions. The design aims to provide a comprehensive set of scenarios to support climate research and policy discussions.