Technical Abstract: Climate change and climate variability has received considerable attention from the scientific community in recent decades and has led to a better understanding of various climate phenomena and driving mechanisms. This increased understanding of climate has prompted engineers and policy makers to ask two important questions: 1) how can an improved understanding of climate variability advance our ability to manage resources such as water, energy, and the environment; and 2) what are the potential impacts on our water resources due to projected climate change? A book “Climate Change, Climate Variations and Water Resources Engineering” has been written on this subject and provides the practicing water resources engineer with an overview of the multiple facets of climate change and climate variability that are relevant to water resources. This first chapter reviews and provides brief explanations of: natural climate variations that can last from a few years to several decades; teleconnections that identify apparent causal relationships between regional climate conditions and ocean/atmospheric conditions in adjacent or remote regions; and, anthropogenic climate change or long term change as a result of human activities rather than from natural causes. The chapter also discusses climate predictability and forecasting, including forecast skill and uncertainty, which are particularly important aspects for planning and management of water resources.