Over the past 35 years, the cost benefit of the economies of scale has led in some industrial production processes to a more than tenfold increase in reactor volume. The article highlights this trend with the focus on three industrial examples: PET production, pressure oxidizing in the mining industry, and fermentation. It gives background information about the current trend and shows industrial examples of the world's largest plants, often referred to as world-scale plants with their specific characteristics, challenges, and mixing and engineering solution.