Environmental quality is a non-excludable public good in that good quality for one is good for all; security may have similar characteristics. The resulting market failures mean that without remedies markets will undersupply. Each consumer has a different valuation that cannot readily be revealed, often requiring public action to remedy. Climate change is the greatest and widest-ranging market failure ever seen, with global long-lasting impacts requiring collective action best addressed by credible global rising carbon taxes that will be challenging to deliver. Policy needs to choose instruments well targeted to objectives, correcting market failures through taxes or standard setting, leaving distributional justice to the tax and benefit system. This chapter argues that the concept of market completeness is helpful in designing appropriate energy policies to address both problems.