Book excerpt: Polycyclic aromatic hydrocarbons (PAHs), or polyarenes, are one of the largest and most structurally diverse class of organic molecules known. High percentages of polyarenes, representing a wide range of molecular sizes and structural types, are present in coal tars and petroleum residues. The major sources of PAHs are crude oil, coal and oil shale. The fuels produced from these fossil sources constitute the primary source of energy for the industrial nations of the world, and the petrochemicals from these raw materials are the basis of the synthetic fibre and plastics industries. PAHs are however, widespread pollutants and their impact on the environment and human health must be monitored and controlled. This book will review and assess our scientific understanding of the ecological exposure and effects PAHs have in different environments and habitats. It will accomplish this by taking the recipients of the pollution in the environment as starting points and working its way back through pathways to access what is required for our understanding of effects and rationale for control. Although this book will concentrate on ecological exposure of PAHs, the general impacts of PAHs on human populations will be touched upon. It is thought to be the first book to focus on the ecological aspects of PAHs.