Progress in catalysis has been, is, and will always be motivated by societal needs (e.g. environment, energy, chemicals, fuels), with the ultimate aim of improving process efficiency on a technical scale. Technical catalysts are often complex multicomponent millimetre-sized bodies consisting of active phases, supports, and numerous additives in shaped forms suitable for their commercial application. They can differ strongly in composition, structure, porosity, and performance from research catalysts, i.e. laboratory-developed materials constituted by a single bulk or supported active phase in powder form, which are the predominant focus of academic investigations. The industrial manufacture of heterogeneous catalysts, encompassing the upscaled preparation, formulation, and structuring, is encircled by secrecy and is decisive for the overall process viability. Yet despite the tremendous relevance, understanding the added complexity of these multicomponent systems and the consequences for the respective structure-property-function relationships has been largely neglected. Accordingly, our review examines the intricacies of the scale up of heterogeneous catalysts. While emphasising the lack of fundamental knowledge we point out the multiple functions that additives could provide by enhancing the mass and heat transfer properties, acting as co-catalysts, or imparting improved chemical, mechanical, or thermal stability. Recent exemplary studies developing rational approaches to prepare, characterise, and evaluate technical catalysts are analysed in detail and new directions for research in this field are put forward.