Adaptation is an important approach for protecting human health, ecosystems, and eco- nomic systems from the risks posed by climate variability and change, and for exploiting beneficial opportunities provided by a changing climate. This paper presents 9 fundamenal principles that should be considered when designing adaptation policy, for example, a sound understanding of the potential regional effects of climate on human and ecological systems is required to target appropriate invest- ments in adaptive responses. The distribution of potential impacts across different populations and the mechanisms by which these impacts occur are also key to effective adaptation measures. Options for coping with climatic changes must be considered in the context of multiple stressors. Further, adapta- tion is likely to exhibit varying levels of effectiveness as demonstrated by current efforts to deal with climate variability. Potential adverse side effects of adaptive strategies must also be accounted for to avoid solutions that are worse than the problem. These issues and others are presented in this paper, with examples from various impacts studies to illustrate key points.