Collaboration has been regarded as a key mechanism in policy implementation and adoption to improve policy outcomes and overcome institutional collective action dilemmas, especially for addressing wicked problems which are complex and unpredictable (Agranoff & McGuire, 2004; Feiock, 2013; Head & Alford, 2013). However, relatively little scholarly attention has been paid to the role of collaboration in the planning and design phases of addressing wicked problems. Because of the crucial role of planning in allocating resources and making strategic priorities for subsequent policy implementations (Bryson, 2018), such an overlook limits our ability in understanding the role of collaboration in the full cycle of policy-making process. Situated in the context of U.S. cities adapting to climate change, which is regarded as one of biggest collective action problems facing human society due to its scale and complexity (Cole, 2005), we aim to contribute to the literature by asking two important yet overlooked questions: Does collaboration with nongovernmental organizations and other government agencies enable local governments to plan to adapt to climate change? If so, how are the effects of these two modes of collaboration different? Climate change adaptation planning at the local government level is chosen because of the leadership role local governments play in climate change actions and the lack of progress in global climate change negotiations (Ostrom, 2010; Swann, 2017).