The proposed Keystone XL pipeline has received considerable attention recently. If constructed, the pipeline would transport crude oil (eg: synthetic crude oil or diluted bitumen) derived from oil sands resources in Alberta, Canada to destinations in the United States and ultimately the international market. Policymakers continue to debate various issues associated with the proposed pipeline. Although some groups have opposed previous oil pipelines -- Alberta Clipper and the Keystone mainline, both of which are operating -- opposition to the Keystone XL proposal has generated substantially more interest among environmental stakeholders. This book discusses the background and the environmental issues the Keystone XL pipeline would cause.