The growing energy demands has led to a soaring level of greenhouse gas (GHG) production, with the implementation of EU legislations, the production of GHG and waste is being curbed but with an economic disadvantage. Multiple industries face losing their competitive edge due to the restrictions currently in place due to the inability to readily burn fossil fuels. With developments of thermal and physical waste management, multiple companies are utilising waste heat technologies to recapture previously lost energy to be used in other applications. The spectrum of papers in this special issue can be split into two main themes recovering energy to be used in other applications such as waste heat recovery applications and thermoacoustic engines and energy conversion via pyrolysis. Such technologies featured in the special edition reflect the growing need for a solution to reduce the production of greenhouse gases but also lower the level of global warming.